Thanks, all. Good suggestions, but this is the problem where you get the "checksum error" on the MT-32 while it the game is sending the SYSEX commands that program the MT-32 for the game-specific sound effects. I read another post stating that the EMU X-Midi Tab adapter has issues in Windows with SYSEX command timing with the older-model MT-32s, and that the problem does not manifest itself on a Mac. I verified this to be the case on my MacBook, so I went ahead and ordered a MIDIsport Uno interface, which was claimed to have no such issue in Windows.
Good news! The MIDIsport Uno arrived on Friday...I loaded it up and it works GREAT with the SYSEX command in DOSBox on Windows Vista x64. So no more having to hook the MacBook up to the big screen to enjoy Wing Commander in all its MT-32 glory.
Thanks for all of the assistance on this forum. Us classic gamers have to stick together these days! 😀
Ian