How much to drive the cans? I think the Xonar's aren't too bad for them, though saying that they themselves are about to release a card with a dedicated headphone amp built in. I can't wait. Goodbye Creative me thinks.
No no not really, the D1's no shoddy card for cans.
What do you need to drive the headphones? The impedance I mean.
If it helps the new card is likely to be ~£200
D1 will be able to drive the relatively low impedance 595's fine.