Too busy at work to say much, but a good friend lent me his DAC1 and Sony SA5000s. They've been making my endless workday very enjoyable (oh I am a sick puppy!). My work setup is generally Mac G5 tower > usb cable > Sonica USB Lan-BGMod > Zu Pivot .5m IC > Portaphile V2 > AKG K501.
Today: Mac G5 tower (iTunes w/mostly Lossless files & some 320AAC) > optical out > DAC1 > 501 and SA5k OR DAC1 RCAs out > Zu Pivot 1m RCA-to-mini > Portaphile V2 or SR-71 > K501 or SA5k via Zu Pivot 1/4-to-1/8 adapter (...adapter just died, so no more of that).
DAC1 is delicious on its own. Surprisingly, P-V2 has nice synergy with DAC1 and tho' it loses the inky black background, open air and super spatiality of DAC1, it adds a fun bit of oomph -- a bit more bass and impact -- as well as imparting rich, lush fullness to vocals and fuller sound overall, and still keeps a good sense of performance space and solid placement of instruments, voices and ambient sounds.
The SA5000s are great. They sound wonderful with DAC1, P-V2, and SR-71. When they hit the market full force and prices drop, they'll be on my list (unless I hit the lottery and buy Qualia and all the other toys in the store...). K501s hold their own, and mate very well with DAC1. Though volume has to be cranked 3 or 4 points higher than SA5000, DAC1 gives 501 rich bass and beautiful, warm and relaxed sound. P-V2 drives my 501s with no problem. DAC1, P-V2 and SR-71 hi-gain seem to have roughly the same output levels.
Since P-V2 drives my 501s so well, I can't imagine much short of K1000 that would have difficulty -- but I haven't studied the stats or auditioned a lot of phones with it, so I don't know for sure. I only know that 501s are notorious difficult to drive well and P-V2 does just fine.
Bye for now.