Pros: async USB, well priced
Cons: none yet
When my m-audio Audiophile 192 soundcard died, I bought an Arcam rDac + Switch-mode upgrade.
Since then my CD's sound like never before. I have started to replace as many MP3's by FLAC's as possible, a difference which I previously found inaudible.
I can't describe the difference in the way that some of you do, but my music contains substantially more "fat" bass and crisp high tones. Alison Kraus + Union Station, Jan Akkerman (MP3), Yo Yo Ma and many others make me shiver again.
(I have also replaced Windows Media Player with J River's Media Center, repaired the amplifier terminals on my Denon UPO-250 amp and put simple rubber door buffers under my B&W DM-604 2S speakers. Changes which also had an audible effect.)