Sim,
Based on your system first question which preamp are you using?
One before I would even entertain getting a dac I would borrow a Innous Zenith and see how much better the Denefrips would sound when being fed an optomized signal.
As other people I think Uberwaltz have commented the standard PC even with a whole bunch of regenerative doodads still doesn't sound anywhere nearly as good as the Zenith.
Second: I would look at getting a great preamp, we are not Backert Labs dealers but have heard their preamps are excellent, and a tube preamp makes a Bryston sound way better.
Third: I would upgrade the Paradigm Sigs long before I upgraded my dac. The Signatures are wonderful speakers but are definatly showing their age vs newer loudspeakers.
Fourth: Power cables and power conditioning are you using any?
Dave and Troy
Audio Doctor NJ