localized sounds - hardware requirements

[BenniSt]

Dear WorldVizers,

we are trying to get spatially localizable sound to work in our VR-Lab.
Now I am look for any hardware requirements to make full use of Vizard's sound localization functions.
What specs would a sound card need to take full advantage of
A) standard sound localization (I suppose that Vizard is using only inter-aural time and and volume differences for that - am I right?)
and
B) the HRTF capability (I read, that you can switch that on somehow and assume you need more high end hardware for that?)

Can recommend any specific sound cards?

Thanks a lot for your help!
- Benni