Head-Fi is the place to go. To get the energy of Rock music into the 650's for not too much $, probably the Gilmore Lite from www.headamp.com would be the best amp. $299 with P.S. upgrade option for another $175 I believe
Head-Fi is the place to go for advice. My advice is to look at Antique Sound Lab. I am using the HD-600 with their MG Head OTL Mark II. It makes the Senns sound sweet yet detailed. I can listen to them for hours. I wish now that I had spent a little more and gotten one of their similar pre-amps with headphone output. I would have made a small second room system by adding am amp and my new Von Schweikert VR-1s. Good luck!
Get a used Wheatfield HA-2 (they're now out of production and hard to find). There's one on Agon now for $600, or if you'd like to wait 2 weeks, I will likely be selling mine for $550 (once I get my speaker amps back, the headphones will unlikely see use for months). You will find no better Senn headamp for rock music, IMHO. Very fast attack, very full sound, and lots of dynamics.
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