i'm new around here too and just got a setup very close to what you're talking about. i have a uDAC feeding a little dot mkIII to power some HD600's.
i'm still racking up my hours on both the senns and the LD, but the sound is wonderful and getting better. it's silky and balanced with a warmish tone, strong but not overpowering bass, fantastic mids and a lovely high end.
the 600 is great at reproducing a wide range of musical material, although i can see how other phones might outperform it within a specific genre. for example, a lover of hip-hop or electronic might want a faster phone with more bass and a more aggressive sound.
one nice thing about the little dot is that it has DIP switches to select one of 4 gain positions, and swapping out the stock tubes allows you more flexibility to tailor the sound to your needs. at under $200, it's also a very good deal. I'm pleased with mine and as many have said, david at littledot is great to work with.
hope this helps....