Guess you didn't find find any variation tones in Duke that'd be of actual use (i.e. it would play back extra stuff on a compatible synth) - just those "driver" ones? That's what I'm still kinda struggling with. So far it really seems that most games follow the "128 GM instruments + GS drums" formula. Very understandable to settle for this as a common denominator.
What I meant by "it plays back the flute" is the following (Tested both ingame w/ DOSBox and standalone MIDI file):
SC-88 GS, MISSIMP.MID: MIDI Player shows a missing instrument at Channel #1, SC display shows the Flute and plays it. No errors.
SC-88 GS, INHIDING.MID: Channel #3 plays the Fretless Bs., Channel #4 shows "No INSTRUMENT" after notes start playing and stays silent. After restarting the level #3 shows the error too. Of course due to the GS reset in the standalone file #3 is fine here.
Internet lore has it that CTF was omitted starting with the SC-55 MkII, so there must be some difference between these cases I listed. I'm not too versed in the technical details, so sorry if my explanations may sound a bit amateur-ish 😉
Now: S-YXG50 plays Channel #4! Same goes for SC-88 set in GM mode. But this is expected, Roland GM mode only plays back capital tones+GS drums. To my understanding they designed this as a foolproof method to play back any kind of unknown material. And perhaps to see how your produced GS stuff would sound on GM devices, heh.
So to sum it up, so far it seems like this particular issue could be resolved by sending a GM reset for SC-55 MkII and up (which take POWER etc. drums) and a GS reset for Yamaha devices (which seem to play back that stupid channel anyway). Confused yet?! 🙄 Also, I find it rather weird that some of those standalone MIDI files have GS resets while the game doesn't have any.
Well, guess at least checking out Windows titles will be a bit more straightforward. If those games just send the MIDI data to Microsoft's MIDI Mapper there is probably not much game driver magic involved.
Edit: Okay, wait... so you found that there ARE different soundtracks for SC/GM here?! 😳 This could render everything I said null and void... can you sketch the differences between those two particular modes after you are done testing? I honestly did my testing here and found them to be identical, so the differences can't be huge. Just AWE vs. GM sounded differently.
Edit 2: It looks like SC mode still doesn't send GS resets. And I still get No INSTRUMENT here as described above. Can confirm the ALFREDH.MID issue though, they fucked it up. It's out of question that STANDARD 2 is intended because this was introduced on the SC-88. Which was out at that time but for obvious reasons I doubt this was the target device. So ironically it'd only fuck up SC-88+, because on earlier devices it'd just default to STANDARD.
A question that occurs to me here is how all of this is handled by source ports. 😀
Also, not entirely topic related, but I had big troubles with GS resets on the S-YXG50 softsynth. Most of the times it doesn't seem to register it. So it can be hard to get correct playback in games such as Duke.