Pre-amp suggestions for Thiel 2.4/Pass Labs XA30.5

I'm not really sure how the Mac autoformers would work with Thiels. For that matter, I'm not really sure I completely understand how the autoformers work at all with the ss Macs. Wouldn't the dB W's go down with the speakers impedance demands, just as they're demanding more? If so, might that make the speakers sound bright? Or would the rather contained impedance swing of the Thiels negate that issue? Other than to keep heat down, what's the point? Wouldn't proper heat sinks deal with that? Would someone please explain it to me?

After saying I wasn't interested in any tube amps, I did run across these guys and become interested... The eastern electric 160W mono-block tube amps:

http://www.stereomojo.com/EasternElectricM156TubeMonoblockAmplifiersReviewtm/EasternElectricM156TubeMonoblockAmplifiersReview.htm

They'd be cheaper than the 250.5 and provide a lot of power for tubes, and come with great reviews...

Also, unsound... in a different thread, I read that the Mcintosh amps (at least the big ones) still double down as impedance drops. So basically, a 402 would give you 400W out of each of the different taps, but if you had a 4 Ohm load on the 8 Ohm tap you'd still pull 800W. It would just tax the amplifier a lot more than if you were attached to the 4 Ohm tap, where you'd be pulling 400W with the same exact load. That said, I don't understand the technology and am just regurgitating someone's anonymous internet post.

I thought the point of the autoformer was to provide the same watts into any load from a give tap? Load tolerant?

A Chinese amp with an unusual tube, that will put out less power than the amp you currently find to inadequately power the speakers your driving? Good luck with that!