Sorry this took so long to get back to you.
I set up a project to test this out.
Synth Rack, loaded a minimoog and SD3 both have presets loaded (lead and classic rock kit)
4 tracks - 2 pairs of audio and midi tracks, 1 pair for each synth
Track Settings:
Track1- Audio: Input: Minimoog Stereo Output - Output: Master
Track2 - Midi: Input: Omni - Output: Minimoog Synth
Track3 - Audio: Input: SD3 Stereo Output - Output: Master
Track4 - Midi: Input: Omni - Output: SD3
I have ZERO trouble playing each sound separately, by changing focus toone mid track or the other.
I have to think SOMETHING is set differently in your project.
Please reply with info like I have placed above, AND email your project to me and I will open it on my system, sub for the VSampler, and try to debug it that way. (To that end, I have sent a private message to you with my private email, and you can attach your project folder - zipped).
It's got to be something - so let's figger it out.
Bob Bone