The change submitted as “2011-11-23 Changes to support multiple busses in hosted AudioUnits” seems to have broken compatibility with at least one popular AudioUnit I have tested (EastWest PLAY). That plugin reports 162 output channels now, which is wrong (and breaks my host architecture). Forcing the number of busses to 1 in the source code fixes the issue (18 output channels).
Possibly EastWest PLAY has 9 busses, but since this information can not be queried from the plugin description (unless I am missing something), how is a host supposed to deal with this extreme number of channels? Filling all these with zeros is a significant performance drain.
Some conditional define should perhaps opt for or against supporting multiple busses? I doubt that every host needs this and since it can break things, it might be better to be able to turn it off.