I highly recommend Pacific Valves Moded Lite DAC 68. I use it in an office set-up for a second system.
It's tube drive using 6922s and upsamples from 16/44 to 24/96 then a second level to 24/192.
It has three switchable inputs. I use it for SAT Radio into the optical and Computer Audio into the S/PDIF. It has an AES as well. Also includes a digital volume control.
After changing the tubes to some nice NOS Seimens CCAs and replacing the PC, the sound is very good. Warm and rich with lots of detail. I have my preamp set to receive the straight audio from the USB converter and then also through the DAC. What a difference.
It costs $700, worth the money