Did you mean you were trying tube amps on the 6XX or 660S? Because the 6XX doesn't sound bright to me. And weird enough, after about 5 or 6 hours of listening, the thin sound that I was hearing got much better. Still using the sound card. "Burn in" does happen in my opinion, because I felt that before (or I think I did)... but never so fast. I'm really excited to get my hands on the new amp/dac, but it'll arrive later in the week. Not sure if I read here on one of your commentaries or somebody else's, about not hearing much any from their sound card and new amp, but it would the bummer of the year considering the CAD535ish it will cost me after border taxes and the hefty shipping cost.