[BradleyC]

 
I am currently looking to finally purchase a dedicated headphone amp for use at work, and need some advice before making my purchase.
 
I am looking to drive a pair of HD650s (which I am about to purchase).  For source I will be primarily using an iPod classic through a Pure i20 dock (all high bit rate of course, ideally I would use the digital out to an outboard DAC), and rarely a PC (so a USB DAC is a plus).  Music style wise, I am all over the place (Indy alternative classic and experimental rock, metal, jazz, blues, folk, house, trip hop, hip hop, rap).
 
My total budget is around $1000-1500 including the headphones (Ideally I would like to aim for $500 to $1K for an amp and DAC).
 
I am currently leaning towards a few options on the amp/dac front:
 
a) Headroom Micro Amp + Micro DAC (Headroom has an attractively priced package including HD650s @$975)
b) Headroom Desktop
c) Nuforce Icon HDP
d) Schiit Valhalla (plus an external DAC)
 
My main concerns are:
 
1) Ability to leave on for extended periods with unattended periods.  Also I would like to avoid a system that needs  an extended warm up time (This is the main reason a Woo WA6 isn't on my list, I have heard that 1 hour warm up is needed).  I am not sure how the Schiit fares in this aspect.
 
2) Good channel balance at low listening volumes.
 
3) Ability to drive lower impedance/high efficiency headphones would be nice but not mandatory.  I also have a set of Shure SE210s, HD570s, a set of noise cancelling headphones from a company that I won't name on an audiophile forum (but they are great for flying)
 
4) Versatility.  In the future I plan to pick up a set of Beyerdynamic DT880, AKG 701 or Denon AHD-5000 cans for when I want a little more brightness, so a bright amp that would pair well only with 650s wouldn't be for me. 
 
5) Cross-feed?  I like the concept of the cross-feed feature in the Headroom amps, some of the older music I listen to has distracting stereo separation.  However I'm not sure if the warming of the tone would be excessive with the already warm HD650s.  I have heard that the brightness filter that Headroom adds to their higher end desktop amp and not to the micro corrects for this nicely.  Can anyone comment on this feature?  The Headroom desktop would be stretching my budget so it would have to be a pretty substantial improvement.
 
Thanks to anyone who can help me out in making my decision....
 
Brad
 
(edited title and text to clarify my budget range)