I use DOSBox on my good computer (Q6600). The P75 is running DOS 6.22. There's no way DOSBox would ever run on that thing...
On the P75, I've got an MPU-401 (an MPU-IPC) I use to connect the MT-32. Prince of Persia uses the MT-32 and sounds great. I believe it also works fine going over the SB16's MIDI/gameport instead of the MPU.
On my real PC running Windows 7 64-bit, I connect the MT-32 using a Roland Edirol UM-1EX USB MIDI interface. Most other games work fine in DOSBox when going that route with the MT-32. BUT, even when not using the real thing and using the emulated MT-32 (MUNT) in DOSBox, Prince of Persia still does not detect the MT-32.