Just posted my review in the TTVJ thread on HF.
http://www.head-fi.org/t/795255/pass-labs-hpa-1-loaner-program/15#post_12334992
TLDR: The Pass Labs HPA-1 is a solid debut from Pass Labs. It sounds clear, punchy and neutral. It was a very nice pairing with the Sennheiser HD600/650/800 trinity. I could live with the HPA-1 as my only amp. Biggest con is the price, which is just too darn expensive for what it is. That being said, fans of solid state amps should definitely give this one a listen.