I'm sure this isn't he most audiophile way of doing it, but this is basically what I'm doing to have 3 separate sound modules connected at once to my PC. I have an MT-32, MT-200, and MT-90 all connected. This is how I have them setup:
I have the Roland UMone USB-MIDI from my PC to the MIDI IN on the MT-32, then use a small MIDI cable from the MIDI THRU on the MT-32, into the MIDI-IN on the MT-200, then another small MIDI cable from the MT-200 MIDI THRU to the one and only MIDI IN on the MT-90. I have all of the modules audio output going into something like this:
https://www.walmart.com/ip/4-Way-AV-Switch-RC … -More/325709139
And then use an RCA to 1/8" stereo cable from that AV selector into my SB Zxr Line-in. Technically all three modules are receiving the same data at the same time, but I only push the button on the one I want to actually to hear at the time. So if I'm playing a Sierra adventure game where the MT-32 will sound the best, I push the button to hear music/sounds from it, and then when I play some Doom I switch over to the MT-200 or MT-90.
Again, it is simple. But it doesn't take up much space at all and just works for what I'm needing to do with only one USB connection from the computer to all the modules and one audio line coming back into the PC.
Midi Modules: MT-32 (OLD), MT-200, MT-90, SD-20