I was noticing that in the Device Manager, the sound driver, National XpressAudio, also contains a PCI bridge. Is the built-in sound PCI based? I figured that this could be why I couldn't hear sound in DOS. There is no National/Cyrix DOS driver that I'm aware of which would be used to setup MPU-401. Unisound shows that all the I/O, IRQ, etc assignments are correct. I've tried the BIOS settings of Enable/Disable MPU-401 and Enable/Disable Joystick.

In Win95, there's no midi sound being output from the speakers if I select to use the External Midi Port in Control Panel / Multimedia. The midi playback progress bar does progress however.

Next, I tried re-installing all the National MediaGX drivers from their all-in-one setup suite, which then placed duplicate audio devices in Control Panel / Multimedia / Devices : "audio devices" and "MIDI Devices". I couldn't figure out how to delete one of these duplicates as removing the sound card device from Device Manager, then restarting, still yielded the duplicate. The duplicate is not shown in the attached photos. Nonetheless, after the existence of the duplicate, paying back the midi file will now hard freeze the system if External Midi is selected from Control Panel / Multimedia.

I've given up on this for now and am using an ISA ESS sound card. Maybe someone else will have better luck. If anyone is able to get the MPU-401 working, particularly with a CHIL & PHIL, could you share your drivers?