"Thanks, Audioengr. The U24 has no other power supply options."
If you open it up and cut the trace with +5V on it and inject your own 5V, then this will do the trick.
"It would seem to me that the future lies in USB DAC's, so that extra step of conversion can be skipped altogether. What do you think?"
Absolutely, although separates like USB to I2S and then I2S DAC input work just as well. USB DAC's, at least the good ones, use this technique. Skips the S/PDIF conversion and clock recovery. The USB DAC that I am designing is simply a USB to I2S converter and a DAC board in the same case. The DAC chips all need I2S or some variant anyway. You cannot skip that part. The best sound that I can offer is using I2S interfaces. 4 DAC's currently support it.
Steve N.
Empirical Audio
Manufacturer/Modder