I do not understand the last post.
Tracks in SONAR do not change type.
Are you trying to add more than one instance of MIDI Guitar?
Or are you trying to drive more than one synth at a time?
Or something else?

I'm guessing some of the interruptions are the trial program 

It converts from audio to midi if I use the input of the midi guitar track.

Yes, the Demo interrupts the sound on a regular basis....glad you got it going MGM. Play around with the setting to get what's best suited for your system......I've gotten mine to work without any latency issues. For me, this was one of the best spent $99....my keyboard playing is very "limited" (to say the least) and this being polyphony is just fantastic for us guitarists.
 
A good thing about the developer is he's been regularly improving the VST's functionality and he does listen/implements a lot of our requests (there's an ongoing thread over at the KVR Forum). 

Next would be finding decent instruments.
What are you all using for keys and horns for example?

MGMitchell
Next would be finding decent instruments.
What are you all using for keys and horns for example?

For keys, I never tried to use MG with it and generally preferred to use my midi keyboard controller to play.....I should look into using MG and find an elegant way to get some good results.
 
For horns/orchestra/synths etc....I use Kontakt and the stuff that came with Komplete 9 as well as 3rd party (Kirk Hunter Strings (Diamond Collection) which has a pretty good horn section). Alchemy & Synthmaster have also been my favourite (for pads and other very cool textures).
 
The beauty of MG is you can use any VST........you just have to spend some time in going through the presets and see how MG/your technique responds to the sounds. Most of them do respond very well.....

MGMitchell
Next would be finding decent instruments.
What are you all using for keys and horns for example?

Actually, I've found I prefer a slightly more synthy sound when playing guitar MIDI. I often use DimPro. Although I do sometimes use Absynth, Omnisphere, or something else from Komplete, the DimPro sounds just seem to work well for me.

Thanks for the leads guys, I'll look into these recommendations.

There's sort of two things here. Using a MIDI guitar as a whole new instrument, or using a guitar as a midi input device. 
The first is the best and most widely used reason for owning one. The second is often because some people never get the hang of using an actual keyboard. 
So you need to keep in  mind what you are after. A guitar synth will never sound like a piano because of the obvious stumming 6 notes VS hitting them at once. 
It is also the a clutsy way of entering drums. PAds work best. 
So for me it's a live controller for synth type sounds and some wind type instruments which are played one note at a time. 
It also seems to work for pad and strings sounds. I love using strings behind a slow balad live. 
I found that MG software had to much latency on my system. I would not spend $100 on it was my thinking. 
My conclusion is either buy a guitar like the Fender or the Godins or give the Fishman system a try. Godin is now using the Fishman on some models. I will be looking at those as I'll have to give my son his guitar back someday..

So is there a way to use my GK3 pickup (that I already have for the GR20) to input directly to midi VST instruments and bypass the "Midiguitar" FX? I assume that would help with latency.