Hello. Looking at the MXDRVg source, I found that there are some keyboard shortcuts that control MXDRV.
By button mashing, here is what I've found so far:
XF3 + OPT1 fades the song out. The fadeout speed is specified with -f when loading mxdrv.
SHIFT + OPT1 slows playback down
CTRL + OPT1 slows it down even more
SHIFT + OPT2 or XF1 + OPT1 speeds playback up
XF4 + OPT2 speeds up even more
XF4 + OPT1 restarts the song
XF5 + OPT2 pauses/unpauses