I recently upgraded my system to OS X Lion and now there are some problems with the midi music in Doomsday(1.9.7 322).
There seems to be a problem with the instrument mapping. The music is playing, but uses at some points the wrong instruments. Some tracks play fine, other are completely screwed up (for example the intro screen music of Doom 2).
I do not think that this is a problem within Doomsday. Other Doom source ports which use SDL also have the same issue.