Interesting feature. I read that paper, Rob, and like his technique for making the amp more heat efficient. On the other hand, I doubt that impedance change will get you "tube" sound in the mid and high drivers. Perhaps this impedance/voltage thingee is there to appeal to tube fans. Many designers over the years have tried to come up with topologies that get the best of transistors and tubes. I'm glad Carver doesn't use tubes in a hybrid amp design. In any event, it looks like a very robust and beefy amp, one that will be hard to clip and should provide high quality amplification and sound .
The only way I know to successfully achieve the "tube" sound Carver is suggesting in his paper is by dedicating a formidable tube amp to drive the mid/highs and a separate SS amp connected to the woofers. If you can get the gains matched and the amps are close enough in phase, the presentation can be superb. I've employed such a setup with a McIntosh MC2102 and a Bryston 4BSST.
On another note, I was at the Montreal Audio Show this weekend and there were hybrid tube/SS amps on display at stratospheric prices which didn't sound good compared to dedicated SS or tube amp setups. Such hybrid amps are notoriously unstable. I once had a 300w Moscode tube/SS hybrid amp which fried my mid and high drivers.
