The search is over! I finally found a Roland MT-32 in decent condition for a decent price.
The MT-32 is a MIDI module from the late eighties, predating General MIDI. Why would anyone want one? That's a good question. In basically every way, modern General MIDI is superior. My new Roland piano plays MIDI with almost surreal realism. However, being a nostalgic guy, I play a lot of old games I grew up with, like the Sierra and Lucasarts classics. They predate GM. They also use a feature of MIDI calles SysEx, with MT-32-specific commands to program instrument information. In other words, those games only sound right on an MT-32.
By "sound right" I mean that they sound fantastic. I hooked up the MT-32 to my laptop via a Midisport USB MIDI dongle and pointed DosBox at MIDI port 20:0. Just like that Space Quest III came to life. It never sounded at all decent on a GM card, so it was fantastic to hear. Next, after fooling around with more of the Space Quest series, I tried a couple of titles from the Kings Quest series, and they sounded fantastic as well. From the Lucasarts side, the Monkey Island games sounded better than ever. I will try some of the Indiana Jones titles later. Of course, games such as Tyrian which are designed for General MIDI sound much better through the piano.
It's also really cool to be exposed to classic Sierra shenanigans I've never seen before. The attached photo shows the MT-32 while Space Quest III is starting. Someone at Sierra decided that the MT-32 display should read "INSERT BUCKAZOID" while the game is starting. Cute.
The closest I've ever heard to these old games sounding right is on my trusty old AudioTrix Pro card. It has a Yamaha chip that fits in quite well with the older Roland sound. However, it's locked into an ancient ISA bus (in my 486), and is therefore not quite "future-proof". I think it's great that I can painlessly use this MT-32 from twenty years ago with modern hardware. This one's a keeper.