Max 6 users are advised to NOT update to Mavericks at this stage. We have found a problem with audio which results in crashing when switching audio on. This will be addressed in a forthcoming Max application update which we shall endeavor to release as soon as possible.
At this point, our testing shows that Live 9/Max 6 based MFL is working fine.
If you have any information for us regarding Mac 10.9 support , please email it to