The Mac's built in convertors aren't going to be as good as those in most audio interfaces
so I'd suggest you look at buying a basic interface. As far as the number of channels on
the interface is concerned, how many inputs and outputs do you need to use at the same
time? If you are never going to be recording anything more than a stereo source and
listening to a stereo playback then a 2in/2out interface will be fine.
suggestion that I would make is, instead of a mixer, have you thought of using a patchbay?
You can just patch in whatever source you want to record to the interface inputs. Of
course, if you are usiing mics then you will still need a mic preamp or two so a mixer may
be more cost effective. If you are looking at mixers then I'd suggest looking ath the
Allen & Heath range too.
JRP Music - Audio Mastering and Restoration.