I owned this combo (aka the stack) before it was released widely to the public. Headroom made 20 of them for sale on head-fi and they were snatched up asap. The dac/amp did drive my hd-580's beautifully, but i purchased it so i could use the stack with my rio karma on the go, but the dac does not work via usb with portables, so i sold mine off.
Great stuff indeed though. Hopefully one day in the near future i'll have a portable source that has a optical out. When my Rio Karma dies i'll definitely try to get my hands on a dap like the iriver H100 series that feature a opt out.
Nick, i'm glad you're into this stuff...you're like a head-fi nut. Do you hang out over there? You would love it i imagine with all the talk of gear and reviews from people who are willing to invest their time and money in new gear. Many head-fiers also set up meets where everyone brings their gear and they audition all types of gear/headphones. It's a great way to expose yourself to new gear.
I think the pic of the stereophile guy was Wes Phillips if he was bald.