If I just want to play my keyboard, I usually will just run the standalone versions of Dimension, Rapture, and Z3tA+ 2. Those all have the "microhost". 

You don't say what version of Sonar you're running or what comfort level you're at with softsynth's, so please don't take offense.

I have a Test project that I use to figure things out and so it I trash it, no problem. 
Why don't you create a test project, add DimPro as a simple instrument track for now, load a patch, with the DimPro track selected, open the PRV, start clicking on the piano keys and see if you're getting playback. If yes, you can draw-in the notes you want or add a midi file to the track. 


After getting use to it, if you're still having problems with multiple synths, let us know and we'll try to help.

Load DimPro.
Make sure a Program is loaded.
Make sure the midi controller is set to midi channel1.  DimPro responds to 1-4 channels if you have it set for multitimbral.  Otherwise, all 4 elements respond to the channel it is set to.
Play.

If it is not loading in a program hit F5 to refresh the browser.  Load from browser.

If still having problems, houston, we have a problem.  it might be install.  I just installed SONAR P on a new 64 bit computer and there is a stranded mutisample folder in C:  It is best to talk to tech support.  This is a user forum, and while generally knowledgable and helpful and well tempered (and handsome, too - well most of us anyway), it can be hard to fix an anomaly.

The first step to helping us help yourself (and practice for tech support) is to list your system, daw and the process you are doing - step by step.
 
PS - tts is a gm synth and probably responds to all midi channels w/ one instance and all notes.  Dimpro responds to a single channel and, depending upon the patch, not all notes.  ONly a dozen keys or so respond if you have a drum, bass doesn't necessary extend above C, and strings and such only respond in their natural range.
@

tKx5050: No offense taken, I have sonar x1 producer -- but I have mostly used sonar 8.5.3 studio with audio tracks. Most midi that I have done has been through a kurzweil PC88 keyboard supplying the audio or the TTS softsynth.

I have done some OK stuff with midi, but it is so sporadic, that I have to relearn everything every time it seems. I did set up a test project in X1 and loaded TTS softsynth and a midi track -- easy.

I am really surprised there are no low-level beginner tutorial videos on using dimension pro with a standalone midi track -- maybe not too many people do that. I have a cheesy midi brass horn section, and I wanted to try and get a better sound from it. hence, I thought I would see what dimension pro had to offer.

AT: Thanks for chiming in. I'll go back to the drawing board and come back when I have a better list of steps. I just figured someone would say "Hey, here's a great video on YouTube -- go watch that" or "everything you need to know in the help file in section xxx". I don't mind figuring stuff out -- I just can't find ANY technical information on how to use dimension pro with an existing midi file. It seems that unless you are playing through dimension "live" all the time, once you have recorded you part, you are using an "existing midi file".

The responses here have been great, though -- it just means I don't really have a good enough understanding of what dimension pro really is. Kevin

I know, I find myself having to relearn certain aspects all the time. If you're triggering from a keyboard the track that receives input is the one that is selected.

Don't know if this will help http://www.youtube.com/watch?v=-2bRI-GP79k 

You need to load a program by clicking on "Empty Program" and then select one by double clicking it in the Browser

Hey I am getting sound out!!! I guess the main problem I had is that when I loaded the dimension pro as a soft synth, I wasn't checking to show the "synth property page" and the "synth rack view" -- so I wasn't setting a program as required.

Once I closed those windows I had the hardest time trying to figure out how to bring them back up! I thought I had clicked on the little symbol that brings that stuff up -- but I guess I didn't.

The good news is it is working. The bad news is that the midi file I have is not too good. I guess I should crank up the keyboard and compose my own horn section. Thanks for all the help -- I knew I was missing just one step in getting started.

Horns?  Usually they are restricted in the range of notes.  that might be the problem if the midi file is playing the notes on a midi channel DimPro ain't set to or if the "range" is off.

But glad it is at least making noise.  That is about all I can do, anyway. ;-)