The'll be enough power for loud volumes , but the sound... Personally I couldn't live long with that lavel of sibilance and metallic presentation... Not to mention the DT990 + STX combo (it's was a real ear shredder).
I haven't hared the 250ohm version of DT880's, but I strongly recommend sennheiser vail for this STX soundcard. It does the trick and makes those senns really great sounding all together.
Edited by AlexRoma - 3/21/12 at 11:12am