OP: IME there is something to an amplifier’s ability to deliver a “sharp attack” of sound. Is that what you mean by a “fast” vs. “slow” amp? Perhaps people who listen to music that features percussive sounds may value an amplifier that can deliver sharp attacks of sound.
Different people have different goals for their hi-fi system. IMO, having a benchmark for the quality of reproduced audio provides a solid basis for evaluating sound quality. For me the benchmark is the live performance of classical music in a suitable venue where no sound reinforcement system is employed – i.e., 100% natural sound.
I listen to classical music and opera. I generally prefer tube amps (particularly 6L6GC), because IMO they excel in delivering the natural timbre of orchestral instruments.
However, for classical music that features piano, sometimes a solid-state amp does a better job of delivering the sharp attack of the piano. For example, Jorge Bolet’s performance of Franz Liszt’s piano transcription of Wagner’s Tannhauser Overture never fails to raise the hair on the back of my neck. (There’s an interesting story about how this “lost” recording was rediscovered. I highly recommend this CD.) IMO the power of this performance is delivered better by my Acurus A250 power amp vs. one of my tube amps (which I generally prefer for orchestral music);
If you listen to music (or movies) that features “sharp attack” … or “SLAM” … that’s a different demand on a hi-fi system than reproducing the natural timbre of a cello.
I own a McIntosh MC 2155 that is in mint condition. It presently drives speakers in my breakfast room and dining room for low-level background music (e.g., cocktail parties).
Several years ago, my MC 2155 was installed in my TV room. I almost never watch action movies. However, several years ago I was watching a movie that featured a soundtrack with “techno music”, and when switching between several amps in this system (at that time) I noticed a significant difference is the amps’ delivery of the IMPACT of the music. At that time, my Pioneer SX-1010 delivered noticeably more SLAM … PUNCH … IMPACT … EXCITEMENT … for an action movie. In comparison, my MC 2155 sounded “slow” … or “dull”. (IIRC, the SX-1010 is direct coupled, vs, the MC 2155’s autoformers.)
This doesn’t mean that I don’t like my MC 2155. I still own my MC 2155. OTOH, my Pioneer SX-1010 is long gone (along with my SX-1980, and SX-1080). Based on the music that I love, these Pioneer amps were not “musical”. (IMO they sounded “dry”.) They were EXCITING to listen to for a few seconds, and then caused a headache. I’ve sold almost all of my solid-state amps, and currently own more than 2 dozen tube amps.
My MC 2155 is not my favorite amp in terms of sound quality. (That would probably go to my McIntosh MC30s, or Scott 296.) Nonetheless, my MC 2155 does a good job driving speakers for background listening. I primarily own my MC 2155 for its blue meters and backlit faceplate. I’m very glad to own an MC 2155 – it’s a handsome amp.
IMO, the $64k questions are:
- What genre(s) of music do you listen to?
- What is your goal for your hi-fi system?
You have to decide what sounds best to your ears, during the duration of a typical listening session. (This is different from what sounds EXCITING for a few seconds).
Does that make sense?
That’s my 2 cents.
Squarepusher isn't for everyone, but he does push boundaries that's for sure. If you read up on that album, he ended up building a lot of the gear himself. For a jazz bass player, he's quite the inventor and electronics wizard. The music is 100% electronica and not really something I listen to for enjoyment, but my son really digs him so I hear a lot of it around the house. Drives my wife nuts 
