Hello, you are correct that the E10 + E9 would give you much more driving power. Not necessary for the HD595, but practically a requirement for the HD650. You can find better and more expensive amps of course, but I don't know anything as competitive price wise as the E9 (barring certain vintage amps) and I believe it is adequate to power the HD650 well.
As of the current time, I would say that there truly is nothing that is "better" than the HD650 in its price range. It just is a matter of preference. I personally like its warmth quite a bit better than the colder neutrality of the other two giants, the Beyer DT880 and AKG K70x, but to each his own. You may wish to wait for impressions on the upcoming Hifiman HE-400 as I am expecting it to have a very good cost to performance ratio. Shure is also going to sell their open flagship soon so this is a very exciting time for those looking for "mid-fi" headphones. Who knows, maybe one of these will emerge as the undisputed performance to cost champion.