Re: mixing issues
I agree with the above.
Audacity is a Non-Linear Editor for audio. It's a freebie open-source program that lots of people use for mastering, myself included.
However, apples-to-apples, you need a DAW.
Editing and mastering are entirely different ideas from mixing.
Dynamic changes in volume, panning (left to right), etc., are things Audacity can't handle (i.e., no saving the moves while you're listening).
Audacity does multiple tracks, badly (you need to time-lock everything together -- clumsy), and it doesn't take controller signals either (from MIDI or anywhere else, for that matter).
Reaper is also available for OSX from 10.5 to 10.11, 32- and 64-bit; see
the website. I'm a Reaper fanboy, but there are plenty of other alternatives.