I had an HD 555 and for a first headphone I enoyed it, but after tried high end AKG (K701/K340) and the MS2 I can't listen an sennheiser anymore. I tried an HD650 on the DV336i and I really don't like the sound
Top of the line Sennheiser is an acquired taste. My comment about Darkvoice amps not doing their best with low impedance phones is true though. It isn't about the sound signature of the phones as much as the output coupling capacitors used in the amp. The capacitors are adequate to drive higher impedance loads but start to audibly roll off on low impedance loads. The DV336 is a great "value" amp when paired with phones it "likes", it's pretty so-so paired with phones it doesn't match with. The difference in pairing is much more apparent than with most amps in this price range. It doesn't take long rolling through phone/amp combinations to hear the difference in the DV336.
The DV336i is supposed to be great paired with an AKG K701/K340, it's really true BUT I prefer the DV336i paired with the MS2, I won't stop to use the DV because some people think the DV is only good with Senn, AKG and Beyer