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
128x128lokie
This is the thread for which I've been looking. GREAT info. I've decided that hard drive to DAC to stereo is the wave of the future and it's here now.
The key is to have a soundcard that has ASIO driver.
That will allow the music data to bypass the whole windows directsound architecture. You will essentially get a bit perfect stream of your data file. (a good rip is obviously the key to have a good data file)

OR

use a USB DAC, like the Apogee MiniDAC.

Either way you will get very good results. (in fact perfect) if your sound card does not have ASIO drivers however, the quality cannot be guranteed.
What about the Xitel HiFi-Pro Link? Rave reviews and it seems to offer the same USB capability plus all the necessary cables. Just the cost of the cables might be worth the $99 price.
Is there a paticular version of Waveterminal that I should look for or just their latest?
I think their latest is the U24.....at least that is what is currently on their interet site. It really is a nice product.