If I were to vote, it'd be for some regular TF2 action mixed in with some regulated play, meaning all soldiers, all spies, Demoknights, etc. Nothing makes a boring old map interesting like mandating classes!
Get an ASUS Xonar DX. It's pretty damn good with my 555s. My settings are 6 channels, headphone for analog out, and S. Rock for the EQ preset. My only gripe with it is that the SPDIF and Mic input are the same port, which really sucks cause now I can't use DDL.
He wants the DG, NOT the DX. The DG has a Headphone Amp built in along with Dolby Headphone processing. Boz
Open-backed a bass-heavy would limit your selection to the Beyerdynamic DT880 and, preferably, the HiFiMan HE-400. Honestly, that's about it if you want extra bass bump, otherwise you'll need to augment your listening experience with some tactile transducers attached to your seating arrangement (e.g. Aura Basshakers). Good luck, Boz