You can get PCI Express sound cards, such as the Creative Sound Blaster X-Fi Xtreme for example. How much would you be looking to spend on a card?
Or you could get a PCI Express wireless card, and the get a PCI Sound card, which would give you more choice in sound cards.
Well, I'll just mention that I think the treble and soundstage is slightly better on the NS1000s when using batteries, even with the FiiO. Wouldn't hurt to try it.
Single AAA. Rechargeable ones would be useful if you have some.