The PaceCar works really well. Some comments I posted on the Empirical Audio Forum:
http://www.audiocircle.com/index.php?topic=62584.msg563537#msg563537
The manufacturer says that his new USB to spdif converter with an Ultraclock comes pretty close to matching it.
That would be the Empirical Off-Ramp 3 which I use with the Superclock 4. Very very articulate with a Paul Hynes SR3-12 power supply and Locus Design Nucleus USB cable. A killer PC audio setup with Bryston gear imho.

Cheers,
Robin