With the HARMONi, OS X is very competent. And OS 9, of course, flies.
I'm trying to get an OS 9 MIDI interface instead of mucking around with GarageBand, which might be suboptimal on this machine anyway. Then I can do everything in ProTools. But this weekend I'm going to get out the multimeter and the soldering iron and patch up the CX5M first while TenFourFox 19/17.0.3 builds.