Just stumbled upon Mixxx!
Its a mixing software just like traktor DJ Studio but for free. I tried it for a few days and it seems very stable on MacOS.
(There is a windows and a linux version too.)
It works perfectly with my M-Audio sound card...
Its not as complete as Traktor but a very good and free alternative for hobby DJ's.
Take a look at it.
i think the next is gonna be that: :P