Pros: Amazing sound, best customer support, great entry price
Cons: a little big for perfect portability
I joined head-fi, looking around for replacement IEMs, and found people talking about headphone amps. After some research, I decided on the PA2V2s and couldn't have made a better choice for a beginner's amp.
I've tried this amp with an iPod nano, an iRiver iH-140 (rockboxed), a Cowon iAudio 9, and a Clip+ (rockboxed), with ER6s, ER-4Ps, and Grado SR80s. The amp warms the sound of the etys, but not to the extent that it distorts their characteristic sound. I noticed a larger soundstage on the Grados.
But the real treat, with all sources and with all headphones is the increased clarity and solidity of the sound. I was listening to Bill Evan's Trio - Live at the Village Vanguard this morning and the amount of detail (the lightest cymbal brush, ice cubes rattling in someone's glass) is ear-opening.
Finally, Gary was helpful and patiently endured many email questions from me as I was making up my mind. He's the best.