I'm looking for a very very very rudimentary "how to" guide that explains how  one should go about modifying a downloaded MIDI file using a SoftSynth resident in X3 Producer.  Specifically I am trying to use a Midi  ... Don't Be Cruel ... and arrange a backing track in an ethereal ballad  type style as opposed to the way Elvis Presley released his version.
 
I use Sonar X3 and import the midi track. Three or four midi tracks are displayed. I create a SoftSynth like Cakewalk TTS1 track and set the midi outputs to playback through that Synth. (As an aside ... when I replace the SofthSynth.  the playback often no longer produces sound).   That's about as far as I can take it.  Is there something out there beside Groove 3 Sonar Explained etc that might help me move ahead in a piece-wise logical fashion?       

I think this is a good question since covers are common regardless of pop music trends. I notice most guides on midi cover either playing midi as-is in a multi-timbral synth or bmp origin compositions. Never came across a good midi rearrangement guide. I have done such tasks but they are tricky. Here are a few simple things I do to make the task easier:

1) Convert midi from one single midi track to seperate midi files for each individual instruments. There are plugins that convert type 0 to type 1 and vice verse. I think there is a CAL that does it within Sonar. This will make it easier to work in terms of individual instruments seperately.

2) Check for events in the midi file that could lead to confusion like program changes. Nothing worse than rearranging a part for a harp and have it change to a tuba in the middle of a verse.

3) I edit the midi files into structured parts. I will identify notes contained in verse and copy to all new midi clip and do the same for choruses, bridges , etc I find it easier to work in parts than whole song arrangements for this sort of thing. It gives me buding blocks that I can always copy and modify to create variety.

4) I avoid using EVERY midi track extracted from the original file. For me, I can create more variety by creating all new tracks based on a central melody or chord progression than by simply copying note for note. Example: say the song has piano, bass, drums and sax. If I wanted to replace the sax part, merely copying and replacing the instrument with trumpet will sound like a trumpet trying to play a sax part. Instead I just ditch the sax all together and just open a trumpet track where I focus on complimenting the piano.

I know that is not scientific or that thorough but they are some of the things that work for me

I feel somewhat vindicated by your remark  "Never came across a good midi rearrangement guide".  I am fairly new to Sonar (Feb of this year).  I've buy backing tracks  that often need to be transposed.  In so doing, the tracks get to sounding pretty bad  especially  in the bass  guitar and bass vocal regions of the scale.  People suggest that I use MIDI files and create my own backing tracks. Hence my search for help.  I am still trying to figure out the lexicon associated with Midi instructions.  I certainly thank you for your prompt and thoughtful response.  I've a lot to learn; but hopefully, once I "break the code"  things will begin to fall into place.  Thanks again!

You won't find re-arranged midi files. The trick is to know enough about music to do it yourself. I don't want to seem harsh but it's true. Once you have the midi and know the key and chord structures, all that's left is to write out what you imagine it should sound like.

I'm one of the few here that have been using MIDI files since 1980's. We had to roll our own and that normally took a whole day just for a drum and bass part. One day someone realized we were all re creating the same songs and the sharing of files started. First locally on our floppy disks, and then way later came the internet at it is now huge. But originally I did about 200 of my own midi tracks, I still use them and over the last few years have been digging into them and re doing them in Sonar. 
 
It blows me away that there are so many free to grab tracks and I have certainly taken advantage of some of this. If I think of a new song I'll certainly do a search first. It's a crap shoot and 1 out of 10 are worth my time. No way I'm paying for a track as then I'll just make my own anyhow.  If the drums are well done it's salvageable. 
Anyhow even the real good ones are wrong for me so I have been editing both my own and download midi tracks for a long time now in Cakewalk/Sonar. 
 
Johnny's really badly written guide to Midi editing crappy downloaded files! The free version! 
Important- OPEN the file, do not import.
As you work SAVE, You can save as a MIDI file but this will not keep your Sonar settings so 'SAVE AS" a CWP file using per project folders.  
 
As you already have figured out it's real simple to open the track and it will play as a GM file using TT-s1. Great starting point. X series have made this simple.  They will sound the way the author wanted them to sound. 
This is all you need for now to work it into your arrangement so leave the other (better) synths alone for now. They come last. 
First thing I do is delete the empty tracks. 
I now solo each track and label if needed and mute all the crap that has nothing good to add. Like the wheezy sax vocals and guitar parts. 
I might at this point go into the event list and see what's up, I'll leave this part out as you might not be that advanced to understand what you see there. 
 
Now I'll change the key. This is easy, Highlight all but Channel 10 the drums. and use transpose. 
And yes, don't expect the Bass part to cooperate. If you think like a Bass player then it's not a problem. But a Song  might have used Low E in the progression and if you think your going to get away with a "-5" transpose without a sub sonic fart for the low B!   
Easy solution is Grab the B's and re transpose +12 now. Sure it's extra work but hey, remember I used to spend a whole day on just a bass and drum track,, you get no sympathy from me... I'm glad it's still takes time.  Suck it up bucko's. 
 
Now the tempo which is super simple unless they used a tempo map so that's a little more work too. There is always possible hidden data like PG changes and tempo so look for this as the song plays. 
 
Now I'll cruise through the song and add markers in the timeline, Verse1, Chorus, Solo etc. 
Sometimes they stick to the original arrangement so it's OK the way it is, but I'll often redo the arrangement and add a better intro and ending. I like my dance songs to end around 3:?? Min.  This is where you learn how to use Sonars Copy/ Paste features. You will learn how to use Select all, Snap to grid, Split, Move over rover and make room. And most important undo!  
That's about it and now I'll make it sound better by Using Session drummer, true Pianos and fiddle with some of TTS-1 sounds too. All you do here is insert the new synth and then go to the midi track and re assign it's output to that synth. Simple. Make sure you load a drum kit into Session drummer or Addictive Drums. 
 
I use real bass so there is an audio track. I'm a guitar player so all I use for backing tracks is Real Bass, the drums and a bit of keyboards. The odd horns and string pad. 
I'm proud of the quality I've acheived using Sonar and now being able to add audio as I've never found a good midi bass sound. 
 
 

Excellent post!!!

I've had to do this on occasion and have had success by just doing the following:
1) file/open into a new Sonar project and save as cwp
2) delete unneeded tracks (melody line, etc)
3) insert better sounding synths and ctrl/drag MIDI data from the TTS tracks to the better sounding synth's track
4) mute the TTS tracks and stick them in a folder named unused (in case I need them later for reference)
5) tweak the newly created tracks

If you're looking to add a string bed--or maybe a hot accordion solo--Band In A Box can generate midi or audio tracks to go along with your midi file.  You can import the midi file to BIAB and generate new tracks in new styles.

Cactus Music, I have been working with MIDI since the 80's also via an Atari and Dr T's software.  Our paths are virtually alike, i.e. all day for one or two parts.  We used to share MIDI files via a BBS, remember those?

I just upgraded to the String Studio V2 and I was really surprised at the good sounding basses in it.  You may want to check that out.

PS - I also play guitar and bass with a little bit of wind controller and keyboard.

I was working with band in a box writing songs for a while. Got a SOP...
 
I was using cubase:
Import the file, select all tracks, open it in list view. find an unwanted event and filter it so those types of events are all you see, like program changes. Then delete them all.
 
Basically deleting everything except note events.
 
Sometimes you want to preserve the sustain on a piano part but not often.
 
Then choose your voices etc.