I never could quite figure out how much processing power was necessary. One thing I know is that there is definitely processing going on with ASIO and SRC. I never could quite get a handle on 16/44 files. Just when I thought I had the right driver, firmware and setting, I would run into an over-saturated sound from a new song.

24/96 files, however, sounded really good. I just don't have that many high res files. Since there are processing involved and more and better programs are surely to follow, I would go with as much processing power as you can get while keeping the machine quiet. Quad core? FYI, I ran Core 2 (6600 at) 2.4MHz and Pentium 2.8MHz and I thought Core 2 sounded better.