Tsk. Tsk.
I am dead set against having multiple subtypes in a Content-Type:. I
don't want to get into using an object-oriented paradigm with
class-inheritance. It will make writing the software too complicated.
I don't think the sound example you give is particularly instructive.
Any machine with a mic and a minimal d/a ought to be able to generate an
audio/basic content. From the receiver's viewpoint, it is immaterial
whether that system was a Sun, a NeXT, or even a Mac.
So, unless you can come up with a better example, I just can't see a
need for multiple subtypes.
On the other hand, use of multiple parameters is less offensive.
Although I'm not keen on the use of parameters either, at least we're
doing customization rather than extensibility, and that is a lot more
tractible.
/mtr