There are two card revs for the MIDIExpressPC. The first production runs were 8 bit (single slot) cards. Then, probably due to the fact that the wanted to use the same card for the MIDITimepiece, the cards evolved into a 16 bit rev.

Motu says there is absolutely no differences in speed or functionality between the two cards, and they will continue to support both.

As of 1/4/96, latest drivers are:

8 bit v1.4
16 bit v2.03 (both of these are both W3.1 and W95 compatible)