I agree, too much warmth with tubes/650. I did like my 650s when I had them with the Schiit Valhalla, but they were significantly more enjoyable through my SS Auditor. No matter what anybody says (and few deny it) there is a slight rolling off of treble at the top, and this is problematic to varying degrees depending on the listener. For some, there is no issue, for others, such as myself, even with a very accomplished and neutral solid state amp (Auditor) I just couldn't get past feeling something was missing. I can only imagine that tubes are going to exaggerate this at least somewhat. Again, please understand this is a very subjective thing and some people may just love the 650s on tubes; whatever floats your boat as they say.
I run my hd650's on the little dot mk3 tube amp, and will honestly say, that the hd650 being a headphone that is dark sounding, my tube amp definitely makes the sound way more enjoyable....I have used my hd650 with a solid state amp, and it totally turned me off...when I hooked it up to my tubes, I was seriously blown away! I never thought in my life that my hd650's could ever, in a million years, sound as good as they do now....on top of that, different tubes will bring a different sound to them
all I can say is, read reviews on different tubes, and you'll be on the path to tube rolling
and you won't believe the results you will get! I currently use a pair of 6HA5 driver tubes, and currently own over $200 in tubes, and took me, after 6 pairs later, to get incredible sound!