MD features a bit accurate OPN2 (YM2612) emulator. We combined it with a SN76489-compatible square wave core (SPSG) and a special emulation of the very crunchy sample playback found in games, and we multiplied all of this by 6 to make it polyphonic in every situation imaginable. A complimentary VGM file player allows you to audition hundreds of vintage soundtracks just like they were meant to be heard.
Plogue's reverse-engineering team worked very hard to make sure that even the rarest corner-cases involving the special features of the OPN2 chip were emulated bit-perfectly, backed by large amounts of testing on special hardware rigs. Add the DAC and impulse-response emulation to that, and you get a degree of realism that has never been reached before!
Oh, and as always, it is done how it should: without using samples!