I am also an owner of Sanders 10c and two Magtechs. After many, many years of buying and selling more amps that I can count, I've settled on the Magtech. It is an extraordinary beast, and about as neutral as they come. To top it all off, they are a relative bargain compared to many of the offerings out there.
I spoke to Roger not too long ago. He is selling a lot of these amps. The conclusion for the lack of used units is obvious. Finding a used Magtech is not impossible. One of mine was just that. Bought it from James Darby, the publisher of Stereomojo.
