I've got my heart set on the ATH-A900 for a new set of headphones, but I'm really on the fence about a new source for them. I don't really need a headphone amp, so the choice is mainly between a USB DAC and a regular PCI sound card. My budget is anywhere up to $100 or so. Anyone want to recommend a good sound card or USB DAC in this range? This would be used mainly for music (mostly metal), plenty of games, and the occasional movie.