That preamp/ amp impedance relation seems an important factor to consider, but so is the amp's output impedance i believe, which is determining of damping which in turn is necessary for large and hard woofers' control. My preamp output impedance is 500 ohms, would an amp input of 10K ohms be fine??
As for class operation, i have used many good ClassA/B and ClassA amps in my life, but i must say that to my ear ClassA has always been superior by far, with a sound as quick and transparent as AB, but adding a more complete, livelier, vibrant and musical sound. I would never accept a soft or sluggish or too warm tube like sound. I want thee sound, the one that is complete, balanced, with full harmonics, highly dynamic, full resolution, neither tuby nor dry, but one which is alive like the real stuff, with the full message, bringing tears in the end!!
I have tried several good AB amps on these Tannoys, but they just look at these amps with disdain, saying; you cannot move me and bring me to life!! In the actual setup, at all times, all ClassA amps (using zero negative feedback) i've tried have always been better. I guess the zero NF issue is an important one too with the Tannoy, which seem to demand the full signal. They are very good speakers, but they are difficult to bring to full blossom, as earlier said they seem to have "unlimited" potential.
I guess the likes of FM Acoustics and other very good AB amps are the exception to the rule, but again the prices are stratospheric. I heard the best of Ayre, very good amps but does not beat the Coincident Dragon MkII, so that would not be an upgrade!! I think Vitus, Pass, Boulder, Gryphon, Soulution and the likes will be the way.
Can we agree on this??