Amp/preamp combo for B&W Matrix 801's

It is hard to give a minimum figure because of the factors mentioned in my first post. As Nick points out the impedance can go quite low, look for an amp that increases its power at low impedances. The M3 is rated at 275 watts at 8 ohms but on test it produced over 800 at 2 ohms with one channel driven. The TriVista, Kw500 and Kw550 all have even more power. These all have nuvistors [very long lived tubes from the military] in the front end. The 308 basic amp has gotten good reviews , it is similar in design without the tubes.

Thanks all, appreciate the feedback.

What about the Plinius line?

I have the 801s VII and use Krell FPB 250 monoblocks and Krell LRCHR preamp with the Krell crossover units with outstanding sound. The croossovers realy make a big difference in sound.

i use them biamped.eagle 2 for the bottom and 2 mc 275 commemorative bridged for the top.
also use a maughan box and happy as a clam.
they are hard to drive with a tube amp running full range although big arc amps do the job decently well.
bass is much tighter with ss amp on the bottom however.