Well, USB could be an option. NI uses it with a 100 MS digitizer.
All of the common interfaces have well defined standards. All have example code on the LabVIEW side and I don't think any are magnitudes more difficult to implement than any other. I have no idea what sort of platforms you have looked at that have no drivers.
How much experience do you have with writing firmware or kernel level drivers? Will this be strictly internal? Do you want laptop compatibility?
