If the MIDI songs for the cartridge where made for a Roland MT32 as you have written, is possible that it wouldn't sound the same on a GM1(General Midi 1), Roland GS(General Standard), Yamaha XG(eXtended General standard), and finally GM2(General Midi 2).
The MT32 was launched on 1987, a lot of time before the GM1 standard on 1991. Roland GS was launched later on the same year(SC55), and was GM1 compliant, but added a lot of non standard features. Yamaha decided to launch the XG standard on 1995, it was a conglomerate, with even the option to switch from the basic GM1 to Roland GS mode and the, for me, superior XG mode.
GM2 was established on 1999 and ended with the MIDI standards "war", adopting some of the Roland only or Yamaha only specifications.
The problem is, the MT32 has the instruments and some controllers on other positions than the GM, so the songs can sound "strange"... But the songs can be re-arranged to sound correctly on a sequencer.
Of course you can opt to buy an original MT32 synthesizer to ear the songs, but the bad new is that the MIDI gear doesn't drop prices with the years, what I can't understand.
