I'm high jacking this thread because my needs are pretty similar. I have a Cakewalk by Roland UA-1G audio inteface. I want to use that as a donor DAC for a DIY tube amp for headphones (currently AKG K172HD and BeyerDynamic DT770-Pro...
The DT770 pros are awesome. Nice long sub bass response, fairly nice mid-range coverage and the trebls are somewhat subdued.
I haven't had a chance to try the others though, so this is just my own experiences.