Hello Plonter, I will be curious to hear your impressions of them with electronic music. I am surprised to hear that they seem to be working better for you with your solid state amp compared to the tube amp. I might have to consider the ultra micro stack.
at first i thought that the headroom rig was lacking in bass so i used the EF1 with a warm tube to get some bass out of them, but now,when they are much more burned in the HD650 sound spectacular with the micros and there is even more bass than with the EF1+mullard.
they right word is "power", a powerful amp is needed to get the full potential out of them and to control them with authority.
In fact,today I got pretty much the best sound I got so far from my rig.
I can't even imagine how they will sound with balanced drive or with much better single ended rig than mine, because the sound was perfect to my ears.