I have KISS modded my hd650, which surprisingly has made the 650 pair okay with SS. The 650 stock din't pair well with any of my amps. I tried the following combinations
Mac (Audirvana) -> Matrix m-stage hpa3u+ -> hd650/he560/k7xx
Mac (Audirvana) -> Matrix m-stage hpa3u+ (dac & preamp) -> ha-200 -> hd650/he560/k7xx
I really like what I heard from the ha-200, it was really euphonic compared. I couldn't shake off the feeling of compression. I have to check if I the matrix -> ha-200 was bad and the signal was clipping.
Btw. how long have you been using this monoblock setup. What dac/headphones are you using?
Did you find it compressed with the HE560 and K7XX as well?
I've used the monoblocks for almost a year but I've got several setups so haven't used it exclusively. In my living room I've got them as well as a Burson Conductor V2+ and Project Ember II. I tend to use HA-200's and the Burson the most though.
After trying out a couple of Dac's I've ended up with the DACmagic Plus paired with the HA-200's. Its detailed and slightly bright signature matches the laid back and smooth signature of the HA-200's really well for my preference. I used it with my tube DAC for a while but it got too warm (and maybe slightly compressed but this was many months ago so I'm not sure) for my liking.
I've got quite a few headphone, please look at my profile for the full line up.