I saw the PC/Mac serial connections and switches on the Yammy and assumed they would be no use to me on any Amiga gear ... but I will watch this trhead and maybe learn otherwise.
Looking at that NOTEMIDI page, it looks like it simply dumps MIDI data directly to the serial port at 38.4 Kbps, so I don't see why any computer couldn't use it with the appropriate RS-232 rejiggering adapters. The one item of concern would be if existing Amiga serial-MIDI software changes the port speed to 31 Kbps; you'd have to fix it to use 38.4 instead, unless the module end is flexible enough to accept both speeds.
I should see if this will work with the similar port on my Korg 05/RW...
If people think this stuff its obsolete or old, then I think vintage Roland stuff must have a bit of a following like the Amiga. This thing was hard to get 
The Sound Canvas line has a huge following in vintage gaming, especially in Japan - a lot of X68000 titles (particularly from Konami) offer a Sound Canvas mode for their music in addition to the built-in Yamaha OPM FM chip.
I've never liked it myself, though (the discrete modules aren't as wretched as the Sound Canvas-derived soundfont that ships with modern Windows, but Lord, they aren't
good,) but Roland has made some pretty good gear in the past. The MT-32 is pretty cut-down compared to the D-50, but by the standards of '80s video game music, it's incredible.