What qualities do you look for in a good amp?

I too was on the "Truly Balanced" path, courtesy of my Rowland Model 2. I even worshipped at the portal of "BPS" (battery power supply). This amp was "IT" for me.
Then I heard an Aleph 3. Class A, single ended, sounds funky on warm up. Heats the room. But on my Apogee Mini Grands, my Montana SPIIs, and my custom 2 way monitors, the Aleph amps sound better than anything I've tried.
Class A means NO headroom, that's OK, I have never clipped my Aleph 2s on my Apogees. 160 watts Class A does not sound at all like a 200 watt class A/B amp. It just sounds better.
I also own an Adcom 5500 stereo amp, this is THE most underatted amp available today, in my opinion. It runs quite hot for a class A/B amp. Nelson Pass had a hand in it's design, & it shows. You can try one of these used for around $600.00.

I've gone over to SET amps, so what I look for isn't so much technical as musical. A liquid midrange without being syrupy, a smooth, sweet treble, and adequate bass extension are fundamentally important. Palpable imaging goes without saying, along with a sense of realism and naturalness. On the technical side low noise is a must, given that the speakers will be quite efficient, and adequate input sensitivity to mate with my favoured transformer passive line stage.

A pretty face, a great rack, and a nice round caboose.

Insightfull answer Gunbei! Let's not forget that all important, head...room. Time for Football!

A nice, thick brushed metal faceplate with deeply engraved logo, and some really slick blue lights and LED's....oh, and those big, gnarly gold-plated terminals out back.....yeah, and those analogue meters to let you know how much g-force they're pullin'. And they gotta be real big and heavy so they aren't dwarfed by my thick, long speaker cables and power cords. Lot'sa them sharp cooling fins too to make it real stealthy looking. And it's gotta cost a butload of cash too, at least as much as your car...braggin' rights and all you know. Oh, and as a consession to my wife it has to go with the wood floors and leather couch.

Yeah, that's the ticket!

Marco