i dunno really. take the can's with you to audition the amp. make sure it works, scratchy knobs is a very fixable issue if you run into that.
watts won't be a concern really. anything will be able to drive the 650's
ive had the best luck with kenwood, marantz, pioneer, sansui, and yamaha. and i've heard good stuff about onkyo and harmon kardon.
really its just a stepping stone. unless you fall in love with it.
i'd just shoot for 70s or early 80s.
and steer clear of black plastic units. some can be good, but a lot of them are not, especially when compared to the older stuff. headphones weren't really a big deal in the late 80s and early 90s.
is your name from the band?
curious, if you're in my area i could possibly point you in a direction