Can you use FireWire instead of USB? The
Focusrite Saffire has AD/DA, mixing, and a lot of different format conversions (e.g., SP/DIF I/O) for a street price of $349. As for audiophile quality, Alan Taffel, who did the series on USB digital audio in the Aug. issue of TAS, much preferred the results of the Focusrite Saffire's format conversion of FireWire-to-SP/DIF over what the Bel Canto was able to do with USB-to-SP/DIF.
And he wasn't blaming the Bel Canto; he just feels that FireWire's additional bandwidth creates a better digital stream. That may also explain why this fairly inexpensive and easily accessible gizmo does 24/192 while you strain to find a 24/192 USB DAC.