Serial lurker here... but felt it was worth comment.
I've been enjoying my HD650's with a Talisman T-35HP for some time now. A spectacularly underrated amp, particularly around these parts...
I tend to rate (and enjoy) amps with a focus on neutrality - and therefore every emotive superlative that seems to stem from that - and a lack of background noise.
I also have a Graham Slee Solo and a DIY M3 both of which I run off a dual tracking DC lab power supply. I like them all for various reasons but I always come back to the Talisman.