Saki70, I don't like the word 'synergy' as it suggests that we are going to balance one defect against another, and I think that in the case that we are talking about, the word is 'compatible' and the answer is 'yes'.
Loop and global feedback are the same thing. Zonal is usually the same as 'local' and may or may not be loop feedback, it could also be degenerative feedback. They are all forms of negative feedback, and there is a lot of verbal shorthand around, so you have to be careful.
I think what is important if you use feedback is that a) the amplifier must be fast and low distortion to begin with and b) the feedback be low enough that the odd-ordered harmonic enhancement is kept out-of-band. That really does not allow for very much feedback in practice.
The ZERO is the only autoformer I know of (we used to make a similar product called the Z-Music autoformer years ago). The concept is all about problem solving- this or that amp can't drive a speaker load that low so here's a solution to that problem. Given that that is the case, they work very well indeed. But if you had a 16 ohm speaker to start with that would be better :)