The PCI-based PC Compatibility Cards are the only cards thats support MIDI devices. Since the Power Macintosh 6100 is NOT a PCI-based Macintosh, you cannot send or receive MIDI data from the serial port using the DOS Compatibility Card. MIDI data travels internally with MS-DOS/Windows, but the data cannot be transferred from the serial port to a MIDI instrument. However, MIDI transfers are fully supported under the Mac OS.
The PCI-Based DOS Compatibility Cards allow you to use the joystick port to transfer MIDI data. Using a proper MIDI adapter, both the MIDI OUT and the MIDI IN channels will be available. This MIDI adapter is the same standard Sound Blaster-compatibile Joystick-to-MIDI adapter that you can find at any MS-DOS/Windows computer store. Apple does not sell this adapter.