This is something I put on my website many years ago after I finally figured out how to do what you are trying to do.
(NOTE: my keyboard is currently set to transmit on midi channel 6 & my interface is a Focusrite saffire. In the info below, FR means my focusrite interface. Substitute YOUR interface in it's place.
The secret to getting the different tracks to play different instruments is to set the OUTPUT to different channels. That channel is applying a different patch or sound and you get the unique instruments on each track. Read the past paragraph below.
ADVANCED TTS set up and operation.
You only need one instance of TTS to be able to play 16 different midi tracks as 16 different instruments. In this demo I will explain just how you accomplish this by starting with 3 midi tracks and one instance of TTS.
So…open a new project ( I opened a normal project and deleted the audio track and then inserted the midi tracks needed and then inserted the soft synth) and insert 3 midi tracks and one instance of TTS. I have:
Track 1 midi piano
Track 2 midi bass
Track 3 midi strings
Track 4 Cakewalk TTS1-1 (audio track this is where TTS lives in this project)
Use the track icons…it makes it ease to know what track you are working on.
Understand that this is just a basic setup of TTS to show you how to setup multiple instruments in one instance of TTS and get it all working.
Set Track 1 (piano)
Input FR channel 6
Output 2-Cakewalk TTS1-1
Channel 1
Key 0
Bank & patch = piano
Set track 2 (bass)
Input FR channel 6
Output 2-Cakewalk TTS1-1
Channel 2
Key -12
Bank & patch = bass
Set track 3 (strings)
Input FR channel 6
Output 2 Cakewalk TTS1-1
Channel 3
Key 0
Bank & patch = strings
A NOTE about my set up..... Notice that all 3 tracks are using the same input....FR channel 6. (Focusrite=FR) This allows all three channels to “hear” the midi keyboard which I have set to transmit on channel 6.
I could set each channel input to a different channel. By doing so I have to change the midi keyboard to transmit on that channel....none of the other channels will hear it, and that can be very useful in recording as you will see shortly.
By setting all 3 channels to the same midi INPUT channel (channel 6) I am able to play all the parts into the three channels with out changing the midi transmit channel on my DX27S. I arm track 1 and record my parts doing the same for the next two tracks. Since the OUTPUTS are set to different channels they are sending their midi data to different channels in the TTS synth. The synth looks at the channel number, and routs that data to that channel and applied the patch & bank info you assigned to it and it carries out those instructions. The result is that you hear 3 different instruments playing from your speakers.
I hope this helps