I recommend Audirvana Plus instead of Pure Music. It's heck of a lot cheaper and sounds IMHO very good, better than 1.86 of Pure Music. IMHO Audirvana v11 beta that I am using with Direct and Integer mode in Mountain Lion is superior to the other music apps I have tried (including Amarra 2.4.5)
I'm still waiting for a proper fix from Pure Music for iTunes11/Mountain Lion before I try it on my Macs.
Another option if you don't need DSD playback, is to get BitPerfect. Cheapest of the lot and sounds very close to Audirvana.
If you already use a Mac, I recommend continuing the use of iTunes. iTunes supports WAV as well, though I find AIFF sounds just as good as WAV while still supporting meta data (album art/artist/track/album details).
I think if you want "high end" sound from the Mac, you will need to put in some work. I downloaded a free copy of an OS X optimization guide from UltraFi a while back and it's now for sale on iBooks. That can help you shut down the extraneous system processes in OS X that aren't needed for music playback. Obviously, this means you shouldn't really use the Mac for anything but music playback. Audirvana Plus has a System Optimizer which is a very easy to use method of disabling some of the background processes but not as comprehensive as the UltraFi guide.
You can also try switching the HDD to SSD and upgrading the RAM to the largest supported. 4GB should be good enough for CD quality, but if you are planning on getting stuff from HD Tracks, I think 8GB should be the minimum.