Rja - the DNA225 has a very high gain (about 30dB -- I owned one long ago), which is probably why you have to attenuate the Berkeley so much. In fact this probably represents the extreme test case for the DAC's attenuation. But this amp also has a high input impedance (~100K). The benefits of a good preamp which Curriemt11 mentions (e.g., expanded soundstage, more 3D images) may involve factors beyond just impedance. I'm not sure what, exactly.