I compared the analogue out (via headphones) of my (modded) 0404 to its digital out and a Meridian 563 and an old 1-bit DAC.
My 0404 doesn't sound thin, that's for sure. A bit muddy perhaps.
The Meridian was slightly clearer and more detailed (but not that much), but the weird thing was the old 1-bit DAC (whilst not being much clearer or more detailed) was certainly a lot sweeter in the mids and treble, and the music seemed to flow better.
Summing up I would say the analogue section is "OK" and holds up fine against most entry-low-mid-fi gear, and offers longevity/future upgrades via digital out. It offers good value for money, only takes up one PCI slot, and is easy to tweak via the DSP.
Sure you can get better sound, but you'd have to go to the Apogee / Benchmark / Bel Canto level to get a real step up from a commercial DAC. I've not heard the NOS kit-DACs, which do intrigue.
Actually, I'll compare it to my Bel Canto later tonight.