If this dac is as smooth as it's supposed to be, you also need to get into what your amp and your speakers sound signatures are and go from there. If I'm not mistaken, I think that a direct connection to an amp is the best way to go. However, the whole impedance mismatch is something to consider when driving your amp/speakers this way. You'll need to do some research on the input impedance of your amp and make sure it's a lot higher than your DAC's output impedance.
Otherwise, an active pre is the way to go and you can't beat the synergy of a system that's voiced to go together like a Bel Canto DAC and Pre combo.
I think everyone has their opinions so do some research and poke around Audiogon, Audio Circle and other forums to see what the latest buzz is. Ultimately, however, only really good speakers are going to yield the differences between high end components. The tube amp sound vs. ss amp sound is the other big distinction to consider.