what is the best, least costly DAC...?

Look at the Musical Fidelity V-DAC. Very good in stock form and better with the "Little Pinky" power supply. I think it does what you want but as I don't do computer music I can't be sure.

I second MF V-DAC. Astonishing value @ $299. Even better with the outboard power supply (Little Pinky, MF own V-PSU etc).

V-DAC does 24/96 but is limited to 16/48 on the USB input so you would have to invest into M2Tech hiFace Asynchronous USB To S/PDIF Converter ($150) to be able to play hi-res files.

I bought one for my sat box, but put it one day in my hi-man rig against dCS Puccini, and to say that I was amazed by this little DAC would be an understatement - I was amazed.

Cannot recommend it highly enough. The outboard power supply of some kind is mandatory IMO.

IMHO, I doubt a V-DAC will improve upon a Rega Saturn...my thoughts would turn toward a Wavelength DAC as a minimum to get near the USB performance you're looking for.

Good listening!

MF V-DAC