I would have to agree with Herman's jitter concerns. I was running a Waveterminal U24 directly into a CAL Alpha (18 bit) dac and then into my Adcom GFP-750 (passive stage). The CAL Alpha was a big improvement over just using the U24's own dac in terms of reducing some of the digital harshness. HOWEVER, I have since picked up a Meridian 518 processor which reportedly has an excellent jitter reduction circuit and also has volume control. So the new chain is lossless FLAC -->U24-->Meridian 518-->CAL Alpha-->Hafler SE-120 amplifier.
I must say that the improvement in sound in this configuration was no subtle change. It is by far the most resolving and detailed, yet analog sounding PC audio configuration I've experienced yet (I've also run an EAD DSP 7000 MK II and Museatex Bitstream dacs in the system). I strongly believe that the underlying problem in my chain was that it was missing a well clocked source - it really made the CAL shine and surpass the EAD and Museatex.
This is all experimental for me and granted, I'm not running the "best" gear in the world. But for now as I wait for technology to mature, I must say that I am quite enjoying my music right now. Hopefully a true one box solution in the near future?
Herman, nice gear by the way.