Which Mc better Mid/High performance in BiAmp set up?

MC1000's..?
You mean two 1000 Watt mono block amps with yet more power for mid/highs ?
And they (a pair of 801N)sounded better with all that running into them ?

Wbs/Bill..

This is what B&W said about my "predicament"

Bi-amping has been observed to improve the performance of loudspeakers, however the benefit will only be realised if identical amplifiers are used for both sections.

If differing amplifiers are used, as in your case solid-state 270w Vs. tube amp 75w, the overall timbre balance and voicing of the speaker will be severely compromised and offer no advantage over that of the single amplifier method - the close knitting of the drive units and integration will be come disturbed by feeding differing performance of sounds to the differing sections of the loudspeakers, the coherency will no longer be seamless, almost disjointed in delivery.

If in doubt, consider bi-wiring which reduces the distortions generated within the loudspeaker circuit, revealing more detail; otherwise masked by the bass drivers associated back EMF.

So..
I was ok selling off my unused un need MA6500 Integrated Amp to get the amp needed to BiAmp..
But I'm definitely not keen on selling off my MC7270 to start from zero as the Amp is excellent.
So how to enhance performance..another 7270 ??
If I was wealthy Id get a pair of MC2000's and see if I like em better but till then..

B&W's advice is very good. They explain the sound that you will get very well. As long as you have an amp that has no problem driving your speakers, and doesn't make any big mistakes sonically, you should bet a much bigger jump in sound quality be upgrading your preamp. It makes a very big difference.