One more note, I can personalty attest to the quality of the Zero DAC. It's pretty fantastic for such a cheep pricepoint. I use one to drive a set of HD650s and it does a great job.
Since you're writing a headphone section I figured I'd weigh on on a few I have played with.
I really like Scheinhizers for their musicality. They aren't the correct choice (generally) for heavy beat driven songs, but they are musical, accurate, have a wide soundstage, and have a nice, clear, "laid back" sound that is the Sennheiser signature.
Also, if you're doing a headphone and soundcard section, make sure you mention the huge advantage that having a card with either Dolby Headphone or CMSS-3D brings to the table for movies. It really is a much more pleasant experience listening to dialogue with either of those two enabled. It keeps the voices from all sounding like they are in your head.
The hd555s are a great place to start, and have nice positional accuracy for videogames, though are a tad base light. I would caution people against the hd595s, I find them to be an odd headphone. The sound doesn't match most of the other Sennheisers, it is a heavier sound.... I really wasn't a fan.
Obviously, for the higher end, the 650s are amazing. With an amp driving them they can literally do it all, one of the most amazing and versatile headphones I have ever listened to, they rival my ascend 340SEs for clarity and sound-stage.
For a more base heavy experiance at right arround 100 bucks, I liked the ATH-A700s, though not as accurate as the 555s, the base is larger and the sound is still nice.
I was less of a fan of the open backed ATH-AD700 version, I found it to be slightly upstaged by the hd555s.
Anyway, just figured I'd weigh in.