Between my Headroom Micro Amp and my Lyr there's nothing even closely similar about the sound of the HD650's. This is no doubt easily explainable (and measurable) by the fact the one is SS and doubtfully has a high voltage swing (but has high current) (and a relatively high output impedance) while the other has a tube section for the voltage with a very high voltage swing (and a very low output impedance.)
I agree though that both had a similar amount of quality and quantity of the sub-bass and both have fooled me into thinking I accidentally had my source running to the big 12" Velodyne subwoofer still (I actually thought the floor was vibrating from the bass...trained response to hearing a certain frequency....meaning the HD650s were outputting similar bass response, to my ears, as my well calibrated sub. I don't call that "bass light" in any way, on either amp unless you're used to a poorly calibrated subwoofer that makes its presence much too known and isn't integrated well with the speakers. People somehow got used to way more bass than reality suggests is needed!
The biggest changes between the amps are separation, detail, a brighter high-end, and a mid-bass that doesn't bloom into the mids. My AVR sounds similar(ish) to my Micro Amp.
By contrast my K702's on the Lyr actually have deeper sub-bass, but have more of a dipp in the upper sub-bass. The result is a "cleaner", "tighter" bass that surprises me with its depth, but doesn't remind me of the signature of my real sub at all. One could argue it sounds like an even better sub, but with slightly too low a crossover for speaker matching.