I played with Retro68 for the work I did on MODTracker, but frankly I'd choose THINK C 5 as it's a much cleaner, direct development environment. It works under System 6 and you can do inline assembly pretty well. You can write your VBL (replayer/mixer) task to work in inline assembly. Assembly stuff can see the 'C' symbols and vice versa. THINKC can do Object Orientation with a subset of C++ features including virtual methods and has a well respected Class Library (TCL) for writing OOP-based apps.
