McIntosh and Autoformers. . .?

What is an Autoformer, and what kind of difference will it make to the sound? I heard some B&W 803's the other day with the McIntosh 402, and it sounded absolutely unreal! I was so impressed, I am thinking of dumping my current SET gear, and going with McIntosh and B&W's.

A freidn tells me that I only want the new McIntosh stuff with the Autoformers. I don't know why. Will the 202 have similar sonic characteristics to the 402? What about the 6900?

Thanks!

B