Yesterday I ran into the first game that would not work with my MT-32 connected through PCMIDI card (The Magic Candle II). Nothing I did could stop the game from freezing on the initial "MINDSCAPE" screen, so I put it aside for a bit and then wondered if it might be one of those rare games hard coded for IRQ2 only. If so, that would mean I'd be completely out of luck, as my bios uses IRQ2 for ACPI.
Today after work I went through the manual for my motherboard to see if I could disable IRQ2/9 somehow, and I found some promising settings and went to work. I was able to free up IRQ9 in the BIOS, so I set the PCMIDI card to IRQ2 and ran MQDIAG, which showed the PCMIDI card on IRQ2. I then launched The Magic Candle II—success! It seems that the game does in fact require the MIDI interface to be set to IRQ2.
It was a bit of a pain, but I'm glad I have the PCMIDI card now set to the default IRQ2/Port330. This should eliminate any other possible incompatibilities I might run into later on!