The current tasks to be done (tickets) are listed on the sourceforge MusicKit Trac Manager.
DSP on non-56K DSP systems. Stephen mentioned he got sound out under OS4.2. However none of the DSP drivers have been ported from NeXTStep V3.3 (as they are all ISA bus cards and I don't know of a PCI 56K card with published interface specs).
A more fruitful avenue seems to be to convert the unit generators to the MPEG Layer 4 structured audio language SAOL [ScheirerVercoe99] and modify the MKDSP framework to download to a supporting card or do the emulation using the native processor. If emulating with the native processor, it would then be possible to use Apples AltiVec vector libraries for increased performance.
For this current revision the .nibs have been upgraded to work with MacOS X and MacOS X-Server and will not load with OpenStep 4.2. The .nibs which are compatible with OpenStep 4.2 are now named nibname-openstep.nib. At the moment you will need to manually symbolically link these to compile for OpenStep 4.2. Eventually Apple's InterfaceBuilder will produce XML based nibs which should reduce the compatibility issue.