Are most DAC's compatible w computers?

I have an SPDIF output that comes directly off my harddrive on my windows xp based computer. I also use windows media. i was thinking about inputing this into a tube DAC to both increase the sound quality and flexibility in my system configuration.
I wanted something fairly inexpensive... I would like to spend $300 or less and have been looking at Cal Labs Sigma II.

Is this straightforward no brainer kind of stuff or is there something that I'm not thinking of... like compatiblity issues?

Thanks,
Doug