So I've chained my MT-32 and SC-88 together, with the SC-88 connected via a m-Audio MIDI-to-USB cable in the MIDI IN receptacle, to my Windows 7 PC with a RCA-to-stereo 1/8" headphone jack, plugged into the L and R RCA outputs on the SC-88, into the line-in/mic port of my X-Fi sound card on the PC.
I then have my MT-32 connected to the SC-88 via two 1/4" audio jacks to RCA connections, each plugged into the L and R RCA connection inputs on the SC-88. A single MIDI cable is plugged into the "Thru" MIDI connection on the SC-88. The other end is plugged into the MIDI input receptacle on the MT-32.
I followed the model displayed here: http://queststudios.com/smf/index.php/topic,3109.0.html
I follow the instructions for games employing MT-32 sound, clicking both the ALL and MUTE buttons on the SC-88. MT-32 sound plays through nicely on such games, and I have no issues.
I'm less clear on what steps I need to take when playing a game with general midi sound. It's seemingly not playing through the Sound Canvas, but instead defaulting to the MT-32, even when the game is set to play GM and/or explicitly set to use Sound Canvas. I've also turned off both the ALL and MUTE buttons, with little change.
When playing a GM game, I am not sure what I should see on the screens of both modules. Right now, it's displaying channel/equalizer bars on the MT-32, and not on the SC-88. Seems to me that when working properly, the bars should be visible on the SC-88, with the MT-32 inactive.
I can just pick up another MIDI-to-USB cable, of course, but would prefer this chaining route.