MIDI splitters are how the pro's do things (Or did when it was the dominant way of controlling instruments) and offers low latency. They're a bit pricey though so you might want to look into building your own if you're handy with that kind of thing because they're not very complicated at all and schematics are easy to find.

I know of no game which needs MIDI In, but that isn't to say such a thing doesn't exist. I doubt any of them "require" it unless they're weird "Learn how to play the piano" games or something.

Never noticed the hanging note bug myself, perhaps I've been lucky and dodged it, then again I rarely control external MIDI devices outside Windows anyway. No doubt other members will probably have better input on these last two questions.

About hanging notes bug on SB, I hear it happens when a daughter boards is present or when MIDI modules are plugged in the gameport.

True. Simultaneous playback of MIDI and DIGI will trigger it. Although you need to read some topics about "legitimate" and "illegitimate" hanging notes and stuff, but in short, YES, all Creative cards are inferior daugtherboard carriers. Some are better than others, especially those with an unbugged DSP version and better SNR, but all Creative cards seem to have cheap buffering and will leave you with a sour taste in mouth when playing Tie Fighter etc....

What about the EMU or OPL FM on the AWE32? Aren't those MIDI devices? I never see those mentioned.

In short, no. Not real MIDI devices if you mean the interface. But they can play MIDI music nonetheless.
OPL purists look for AWE models with a real OPL3 chip on them. Some SB16 models have them integrated.
Technically, OPL is addressed by its own port, 388h usually, so it is not even an UART MIDI device.
Avoid the CQM of the AWE64 like a plague.

EMU8000 is a Proteus-derived synth, but has poor DOS support. In order to "emulate" a real daughterboard or external synth (work at standard addresses like 330h or 300h) you need redirection (AWEUTIL) which has severe restrictions.

I read there are differences between a Roland SC-55 and a Roland SC-88.
I own a SC-88VL, and it has a button that reads "SC-55 MAP" on it.
Is that for SC-55 compatibility?

Yes.

MIDI splitters are how the pro's do things (Or did when it was the dominant way of controlling instruments) and offers low latency. They're a bit pricey though so you might want to look into building your own if you're handy with that kind of thing because they're not very complicated at all and schematics are easy to find.

Splitter on its way!

True. Simultaneous playback of MIDI and DIGI will trigger it. Although you need to read some topics about "legitimate" and "illegitame" hanging notes and stuff, but in short, YES, all Creative cards are inferior daugtherboard carriers. Some are better than others, especially those with an unbugged DSP version and better SNR, but all Creative cards seem to have cheap buffering and will leave you with a sour taste in mouth when playing Tie Fighter etc....

I did, apparently one of the best cards I can get is an AWE32 CT3900, so I'm getting that.
That one is reputed to be immune to type 1 hanging note bug if I believe the article here http://www.vogonswiki.com/index.php/Hanging_note_bug.

In short, no. Not real MIDI devices if you mean the interface. But they can play MIDI music nonetheless.
OPL purists look for AWE models with a real OPL3 chip on them. Some SB16 models have them integrated.
Technically, OPL is addressed by its own port, 388h usually, so it is not even an UART MIDI device.

Aaah that's why those are never mentioned when talking about hanging notes bug.

Avoid the CQM of the AWE64 like a plague.

Yes sir, that I will, without a doubt.
I've heard my share of weird stuff with an AWE64 Gold, like for example missing speech in Silent Service II.
I believe I got rid of all that CQM stuff years ago!

So this concludes today's round of questions.
I got a "cheap" vanilla SC-55 module that looks covered in seagull vomit (but is in great working conditions, if I am to believe the seller) from Germany, it hopefully it won't get stuck for months in customs.

Thank you both for your help!

I just had an interesting read that made me even more confused than usual here: http://nerdlypleasures.blogspot.com.es/search/label/MIDI

If I get this straight, an earliest SC-55 isn't compatible with GM so a GM reset is the same as a GS reset, but has this capital tone feedback feature.
Later revisions have a different map, are 100% compatible so they will react the way one would expect to a GM reset, but don't have capital tone feedback.
Forcing a GM reset on such an unit would disable variation tones on games supporting it.
It's getting more and more confusing. I have a SC-88VL and I purchased a SC-55 this morning, which appears to be an earliest revision (GS STANDARD logo from what I can see).

Right now I'm planning on these things:
MT-32 old rev with no jack;
CM-32L which, by dumb luck, appears to be a ROM v.1.02, but I don't know for sure (ROMS appear to be soldered on the PCB and there are no stickers on them)
SC-55 first gen or SC-88VL

Should I have both SC-55 and SC-88 connected at the same time? Where can I find a list of games supporting first generation SC-55 capital tone feedback?

There are a couple of games that make use of MIDI in, but not on the x86 PC. Two or three on the Atari ST line, and I think one on the Amiga that came with some Casio midi kit and keyboard. It's been 20+ years since I have seen these things so I can't remember details. I'll leave that to our resident experts on those rigs. I wouldn't not be surprised to learn that there may be a game or two for Yamaha's CX5 line (MSX computers with MIDI built in).

Completely irrelevant, but didn't the Atari have MIDI Maze?

Edit: Yeah, it did. 16 player FPS using a kind of "MIDI Loop" as a network. Supposedly a PC version reached prototype stages but was never completed. This is the only game I can think of (outside of the previously mentioned keyboard playing stuff) which would use it, and as it isn't on the PC it isn't really relevant. Still a point of interest though.

I suppose all this MIDI stuff could be used by emulators.
That opens all sorts of possibilities, as if it wasn't complex enough on a single machine (PC).
Wasn't the Atari ST the prevalent machine for everything MIDI back in the 80s?

I can remember https://en.wikipedia.org/wiki/Jean_Michel_Jarre
going on stage with all sorts of weird and strange electronic stuff, and a ST was usually part of the show!