OK Larry, you sold me on the HD600's and NuForce uDAC. I really like the combo with my laptop and the detail is great, but they break up when the music gets complex.
What amp do I need to get? Everyone seems to like the Woo Audio WA6. I'd rather avoid tubes because of the warmup time, but then again, SS needs some warmup time too. Anyway, how about some suggestions in a few price ranges, say $250 or $300, $400 and $650.
And am I going to have to get a different DAC? Remember, my source is MP3's from my server (of varying bitrates).
For $169 an EF2 or Qinpu A-3 will add power and soundstage over the uDAC, but they wont be your final amp.
In the $250-300 range for HD600, for an audible upgrade over the uDAC headphone out I would look for a used Cavalli CTH, head-direct EF1 or Dark Voice 336i with upgraded tubes. Or a Travagans Red with AD743 or OPA627 opamps for an SS amp (Cute Beyond with upgraded opamps might substitute, but I haven't tried one with upgraded opamps). These are all on a similar or very slightly better level than the Apogee mini-DAC built in headphone amp.
In the $400 range I would consider a Grahm Slee Novo, but plan to add the PSU1 upgrade at some point. Next step up is in the $620 - $690 range would be a Woo WA6 or Grahm Slee Solo SRG II. Any of these could be your last amp for a while, and they all represent a nice step up in power, detail, soundstage and refinement. I am evaluating the prototype Nuforce HDP DAC/amp and for $449 it may be a real contender too, but the headphone amp burn-in is only about 1/2 - 2/3 of the way done. With the HDP you'd be able to sell the uDAC to recoup some of the cost.