KrisM
2
Do you want the option of recording all outputs at once? You’ll need an audio interface with a lot of inputs. OS X can let you aggregate multiple interfaces and treat them as one; I don’t know if Windows can do this or not, as I haven’t used it since XP.
If you’re happy to use the mixer or don’t mind recording 1-2 tracks at a time, then don’t worry about it and get the best converters you can in an interface with stereo line inputs. You don’t even need a MacBook Pro for that, an Air will suffice.
Laptops generally aren’t as bang for the buck as a desktop, and PCs are cheaper as a whole (I have an iMac and MacBook Air, btw) than Macs, but a good PC laptop will still cost a lot depending on what you want to do. Neither OS is going to be better than the other, so don’t worry about that.
If you just want stereo inputs, I’d be absolutely comfortable recommending the RME Babyface (very solid drivers and great latency) and a MacBook Pro if you want as much CPU you can get in a portable Mac.