I just did a bit of a job trying to get better audio from my PC, so this might help you.
I got closed phones, AKG 271s, which are fantastic. Running them through the headphone out of my PC, they sound great, despite the sound card being a standard on-board AC97 card on an IBM Netvista. Having spent far too much of my time here I though "ah ha, I can make that sound better".
I got myself an m-audio sonica theatre and a PIMETA, and sourced a power supply locally. After a good deal of waiting, with great anticipation I plugged them in and set them up and.... there was no difference. $300 worth of equipment, and it sounds the same.
I'm not sure if there's something wrong with my system, or maybe my PCs AC97 sound was great to begin with. My main point is that unless your PC sound is sub-standard you could be wasting your money. You might be better off going for better quality headphones than going for the whole source/amp solution.
There are a few problems with the bithead/total bithead at the moment, but HeadRoom are working to fix them, and will replace the existing units. Built in crossfeed is a bonus too. This is consistent with their reputation for providing good products and great service. The early reports are that they sound great. If I had to upgrade my PC sound again, i'd definitely wait for the new revision and get one of those instead. With the 30 day right of return, you've nothing to lose.