Sorry for the late response - you can also contact me directly trough [my username]@gmail.com.
You can use it with other Processing libraries, if you include these libraries (*.jar files) in the appropriate directories. Matlab has a static classpath (edit classpath.txt), and MaxMSP has a directory (see readme.txt).
However, I have had problems with OPENGL, since they also use native libraries (*.dll files) and not only *.jar files. I don't know if its possible in Matlab/MaxMSP - that depends on how they set up their JVM.
I was using Max5 with windows64 at the time. Everything was running properly, although I had the idea that MaxMSP did not dispose of the Java classes properly. (So, if you would delete the max object, the processing sketch would still remain in memory somewhere if you didn't dispose of it...)
I do remember MaxMSP crashing at startup when working on that project. I had to delete the preference folder to fix it. I don't know if that was related to this. (and why that error occured).
So I am afraid I can't help you out! Did not use Max6 yet....