I read:
I'm looking for a multichannel sound mixer built in PD for OSX
for the mixer try console from http://www.swiezinski.de/pd/
which allows to play multiple soundloops .... and synchronized and and has the possibility for oneshots...
this goes far beyond a mixer but I guess most of the pieces have been built, for loop control I suggest you patch together what you find in doc/3.audio.examples, since it's probably the only way to get all the features you want - the features you don't want + a gui that you are comfortable with.
regards,
x