IMO (mac or otherwise) - there is no good way to post matrix two tracks (yet)...A/D clock drift is the primary obstacle.
No two sources will align perfectly, one will always drift out of sync with the other.
Teddy posted some stuff the other day - but we need something simpler, that really addresses this one particular issue.
There a some different hacks that minimize the drift, and some folks use a "stretch" function in a certain software...( I forget which)
It seems like there has to be away to compare and sync up the clocks from two waves - So the files will be consistient timewise...