Andreas, the C270 is worth considering. I'm using the preamp section of a NAD C340 integrated and a NAD C270 power amp to drive Vandersteen 1b speakers, after having used the C340 alone. Adding the C270 made a noticeable difference in the bass presence and depth, and in the sound of my system overall. The 1b speakers sounded good to start with, but seemed to respond well to the power increase. Even if I replace the C340 with a preamp at some point, I might hang onto the C270 for a while longer, as NAD power amplifiers have a good reputation. While somthing like a McCormack DNA-125 might offer better sound, it would be at a higher price level.
