You take a very scientific approach our approach is via actual listening
Sorry, but I take both. As they are equally important.
And anyone recommending any amp should do also.
Hoping to learn more.You may get an amp that behaves like a tone control into the Kef's difficult load instead of doing what amps should do, "maintaining a flat frequency response regardless of load variations".
Like this one, the wavy top line is what it’s frequency response is like into an easy "simulated Kantor" speaker load, far from flat!, it will be even worse with the Kef’s as they are harder to drive than the Kantors, this is what behaving like a tone control is meant.
https://www.stereophile.com/images/archivesart/V10FIG02.jpg
Cheers George