So the final Q is, can I do full duplex with ALSA/oss emulation of OSS/free, with very little latency in Jmax and PD?
I guess I will tell my opinion here and it's not aimed to be the final statement for "Pd vs Jmax". I've got both installed and i'm rather using PD which scarcely provokes clicks or latencies, sorry for jmax...it does. This is essentially due to the fact that jmax uses a Java's GUI which is way slower from the PD's GUI using TCL/TK. Of course, many paremeters have to be tuned to make PD and jmax work the best way on your system ( frags for PD,..... ) but, once this is done, PD is proved to support much more complex patches running together.
Concerning ALSA, the sound is generally speaking of a better quality and it supports full-duplex.
cheers,
Yves/
PS : anyway, you don't have to choose between PD and jmax, both can be used at the same time on a good machine.