For anyone who is struggling to set up the Garritan Personal Orchestra inside of Sonar X1, which I just finished doing, here is a more detailed version of the excellent instructions that were posted a while back by browser (in February of 2011), fleshed out with some additional details I noted along the way.
Specifically, this pertains to GPO with Aria Player 1.02, and Sonar Producer X1d Extended. (Might apply to other variations as well; I don't know.)
It is assumed that you have already INSTALLED Garritan Personal Orchestra (with VST driver) on your computer, which is a separate adventure...
If I've made any errors in these instructions, I'd appreciate it if you'd ping me about it.
 
IN SONAR…   
             Create a new, "Normal" Project. Then...
 Insert/Soft Synth/VST/Aria Player Multi VST.
In the “Insert Soft Synth Options” dialog box that opens:
                select All Synth Audio Outputs – Stereo
                In the “Open These Windows” section, select Synth Property Page
                In the “Display Automation On:” section, leave it set to First Synth Audio Track
          Click OK
 
Sonar creates 16 “Aria Player” tracks and opens the Garritan Aria Player window
 
IN SONAR…    
Create 15 more MIDI tracks (Insert/MIDI Track, 15 times)
You’ll probably find it useful to relabel each of the MIDI tracks, so that they’re
        not just “Track 19, Track 20 (or whatever numbers)”, etc.
        I relabeled mine MIDI-1, MIDI-2, MIDI-3, etc. This will be convenient later,
            because each MIDI track will have a name (number) that corresponds
            to one of the 16 channels of the Aria Player.
       Then (still in SONAR) do this for EACH MIDI track:
               Select a MIDI track by clicking its Track Number.
               In the Channel Strip for that track:
                         In the IN/OUT section at the bottom of the strip…
                               (I THINK the following sentence is correct:)
                                  Set the INPUT to the "Omni" setting
                                   of your external MIDI controller
 
                                For OUTPUT, select the Aria Player   
                                Underneath the FX Bin  near the middle 
                                 of the strip… 
                               Click the “C” button pulldown, and select
                                the numbered Aria Player
                               instance that corresponds to the MIDI track number you’re working with.
                               For example, in my track MIDI-1, I select “1. Aria Player Multi VST”
                                                        in my track MIDI-2, I select “2. Aria Player Multi VST”
                                                   …and so forth, until each MIDI track is assigned to an
                                                      individual instance of the Aria Player
IN THE ARIA PLAYER INTERFACE…   
By default, the name of each of the 16 channels in the Interface window  says “empty”
 If you don’t see the channels, then click “MIXER” in the right-hand panel
             of the Aria Player window.
Do the following for each of the 16 instrument-channels in the Interface window:
      In the grey strip underneath the instrument name there are four items.
                 The third item from the left is the Aria Player’s “output pair”.
                 By default, the output pair for every channel is “1/2”
                CLICK on the “1/2”, and an “Output” menu pops up.
                Select a sequentially different output pair for each individual instrument channel.
                     For example, channel 1 should be set to output 1/2,
                      channel 2 should be set to 3/4, and so on, ending with channel 16
                      being set to 31/32
IN THE ARIA PLAYER INTERFACE…   
In each of the 16 channels (if you’re going to use all 16), select the instrument
       you want in that channel. I did it this way (assuming all your instrument channels
       are currently empty):
         Click on the word “empty”
         This pops up a menu. In my system, the bottom item in the menu is GPO
              (for Garritan Personal Orchestra). Select that.
        In the little 2-item menu that pops up next, select “Standard”
               Select the category you want from the category menu.
               Select the specific instrument you want from the instrument menu.
               The Aria Player loads the instrument, and its name appears in the Player window.
 
You might want to save your configured Aria Player as a Preset… to do this, double-click the field next to the word “Presets” at the top of the Aria Player window, then type in a name for your preset, and click the disk-icon to the right of the field.
 
IF YOU’RE USING AN EXTERNAL MIDI CONTROLLER
           (as opposed to entering notes on the computer)…
                 You can leave your MIDI controller set to channel 1.
           When you click on the track number (not name) of one of your MIDI tracks
           (in the SONAR interface), your MIDI controller will play the instrument that
          you assigned to the Aria channel whose number corresponds to the MIDI
          track you selected. (For example -- if you named your MIDI tracks sequentially
          by number -- then when you click on whatever SONAR track number belongs to
          the track you named MIDI-1, your MIDI controller will play Aria’s instrument number 1.)
 
STRONG RECOMMENDATION: After you’ve gone through all this trouble, SAVE the complete
      configuration as a Track Template  (in SONAR:  File/Export/Track Template).
 
CONFUSING ADDITIONAL NOTE: After I had successfully done all of the above and recorded a test-song or two, sometimes subsequently when I would reload one of those songs, and/or create a new song from my saved template, things would get all screwy. My MIDI controller would trigger a sound completely different from instrument on the MIDI track I selected. If I later reloaded the song again and/or set up a new project from the template again, it would work correctly. I have no idea why this happens. Possibly has something to do with GPO’s handling of computer memory(?). But I don’t know.

(deleted this addendum -- I realized I could edit my original message)

Logging some of the things that fit in the "screwy behavior" category...
Sometimes (not always), after I've set up everything just the way described in the instructions above, then when I select a MIDI track (for example, the track that is assigned to MIDI channel5), then when I play my external controller, that instrument in the Aria interface responds, but INSTRUMENT NUMBER 1 ALSO RESPONDS. I've tried this with several different tracks, and in each case, the selected track responds, but instrument 1 tags along for the ride.
So for instance, instrument 1 is a harp and instrument 5 is a saxophone. I select the Sonar track that has MIDI5, and play my controller -- the result is a nice (but baffling) mix of harp and saxophone.
 
Haven't yet figured out a pattern to this. I've had at least a couple of sessions where this does NOT happen... ie, instrument number 1 minds its own business & doesn't butt-in when I'm playing something else.

thanks for taking the time to do this

I set up slightly differently, using an external MIDI keyboard. I assign different channels to the MIDI tracks in the input section at the bottom of the channel strip, rather than under the FX bin. Then I switch MIDI channels on my keyboard to play the various instruments. I think your way of doing it is better, because the track you want to play has to be highlighted anyway, so there's no reason to assign different MIDI channels to the tracks.

THANK YOU!!!! I was about to pull someone else's hair out!!!  :P

I always leave the midi input set to omni for midi tracks, and when setting up multiple midi tracks that will drive multiple instruments loaded into say Kontakt 5, I assign the appropriate midi channel in the dropdown just under the FX bin for each midi track.
 
It is all then controlled by whichever Echo Midi On buttons are lit.  Sonar, by default, will automatically light the midi echo on button for a midi track when it is brought into focus.  That then will cause that particular synth or individual instrument in a multi-timbral synth to play.
 
If I want to hear a layered sound, I then manually click on additional echo midi on buttons and then multiple synths/instruments will be heard.
 
Bob Bone
 

Thanks for sharing Ernie! I haven't done an orchestral thing since I upgraded to GPO4 and X3e PE. Hopefully I can try something and post back here as to the results and your work/efforts.
Michael

Took me awhile to see that this is a very old thread, from March 7, 2012 in fact - But I'll join in since in the original thread, ernietamminga, the OPO, said:

"...here is a more detailed version of the excellent instructions that were posted a while back by browser (in February of 2011)..."

"browser" is the common typo for my user name "rbowser" - He was referring to a post I apparently wrote three years ago!

This thread was revived by GBO323, since it looks like he was searching for help on setting up GPO.  

Do you have it all going on now GBO323?  Setting ARIA/Garritan up relies on the same basic principles of setting up any multi-timbral synth/sampler.  When that's a new process, it can be a bit of a struggle, as ernietamminga was saying.  I've used GPO for so many years now that it's second nature - I'll set up a new project in just a couple of minutes, even without using templates, because it's as engrained in me as turning on a water faucet.  That's the way all this kind of thing becomes after repetition.

Now with the combination of old and new posts on this thread, I wanted to insert a few things:

"...After I had successfully done all of the above and recorded a test-song or two, sometimes subsequently when I would reload one of those songs, and/or create a new song from my saved template, things would get all screwy. My MIDI controller would trigger a sound completely different from instrument on the MIDI track I selected. If I later reloaded the song again and/or set up a new project from the template again, it would work correctly. I have no idea why this happens. Possibly has something to do with GPO’s handling of computer memory(?)..."

I wonder if ernie's still around - I'd like to know if that kind of problem kept happening even after he became a more experienced GPO and Sonar user.  What he's described there has literally never happened to me, not in 9 years of using GPO.  That's a very odd behavior he was experiencing.

Ernie's steps for setting GPO up seem essentially right.  He describes setting up all the MIDi and audio tracks in Sonar, and loading instruments in ARIA.  Then he says something confusing, since up until this bit, he was talking about setting up a single instance of ARIA with 16 instruments.

"...and so forth, until each MIDI track is assigned to an individual instance of the Aria Player ..."

He probably meant "until each MIDI track is assigned to an individual slot in ARIA."  He was correct that each track can be directed to a different instance of ARIA, but before that sentence, he hadn't been talking about multiple instances.  Just potentially confusing to newbies trying to follow the instructions.

He also sed:

"...You’ll probably find it useful to relabel each of the MIDI tracks, so that they’re not just “Track 19, Track 20 (or whatever numbers)”, etc. I relabeled mine MIDI-1, MIDI-2, MIDI-3, etc..."

You definitely need to re-label the program generated names for tracks - But why replace the track numbers with MIDI numbers?  The best thing to do is to just type in the instrument's name.  You'll know at a glance what track is controlling what instrument.

Later he sed:

"...Sometimes (not always), after I've set up everything just the way described in the instructions above, then when I select a MIDI track (for example, the track that is assigned to MIDI channel5), then when I play my external controller, that instrument in the Aria interface responds, but INSTRUMENT NUMBER 1 ALSO RESPONDS..."

Bob Bone's new post addresses that:

robert_e_bone...I assign the appropriate midi channel in the dropdown just under the FX bin for each midi track.

It is all then controlled by whichever Echo Midi On buttons are lit.  Sonar, by default, will automatically light the midi echo on button for a midi track when it is brought into focus.  That then will cause that particular synth or individual instrument in a multi-timbral synth to play...

--I think Ernie was having the doubled instrument problem because of accidentally having activated the Echo button on his first instrument's track.

Alkemy realized from reading Ernie's posts that he'd been setting the MIDI output of his keyboard incorrectly:

alkemy "...I switch MIDI channels on my keyboard to play the various instruments. I think your way of doing it is better, because the track you want to play has to be highlighted anyway, so there's no reason to assign different MIDI channels to the tracks..."

That's something that often comes up - People thinking they need to laboriously change their keyboard's channel each time they want to hear a different instrument.  Therein lies the path to madness!  Bob Bone reiterated what Ernie said in his original post - You set a specific MIDI Channel for each track in its header (inspector) and then when that track has focus, that's the instrument that plays - the one on the same MIDI Channel in ARIA.  The keyboard can remain on MIDI 1 - it doesn't matter.  The track settings are sending the data that's needed.  That's why in the PRV, if you haven't done any bouncing, you'll see Channel 1 listed for all the controllers - that's the original data sent by the keyboard, but the track settings determine what channel that data is actually sent out on.

And - so forth!

Interesting to see this come to the surface again.

Randy

Randy...yep, I was looking for the "how to" cause I was close to frustration.
 
I did get it set up. The only hiccup is on the second track, I keep having to re-load the Choir in Aria *every* time I re-start the track. That's annoying. Any ideas on that one?