Autoformer vs Speaker impedance Curve

an Autoformer would work, because it’s one of the only speakers that presents a very benign 3-4 ohm impedance load.

This statement ignores the fact that loop feedback compensates for this sort of thing.

Loop feedback compensates for the autoformer

How the designer set up the amplifier with the transformer plays a big role. The reason you do this BTW is to reduce distortion- all amps have higher distortion playing lower impedances, so if you can raise the overall impedance seen by the output devices distortion will be reduced. This is why Mac uses autoformers. 

Autoformers reduce distortion

Since all forms of loop feedback are known to add higher ordered harmonic distortions as well as intermodulations.

Loop feedback causes distortion 

Okay.  Got it:

Autoformers reduce distortion but need to be compensated for with loop feedback which adds higher order harmonic distortion...the worse kind!  🤯

Sorry, couldn’t resist having a bit of fun with this!  🤪

I’m sure the interplay between these forces is well beyond the scope of this discussion  and certainly well beyond my very limited knowledge.

Thanks all for your input!  Much to think about.

Rob 

This statement ignores the fact that loop feedback compensates for this sort of thing.

This statement ignores just how much loop feedback is needed to fully compensate for this sort of thing. We all know what too much feedback has the reputation to sound like.
And also ignores if there is no global feedback just local feedback which many good amps use, as well as some amps that don't use feedback.

Like I said before  73max OP  your better off using an amp that is right for the job, and not spending money on autoformers, better spending it on the right amp instead which your B&W 802D3 deserve.
 
Cheers George  

 your better off using an amp that is right for the job

 ...such as?

...such as?

With this kind of impedance and phase angle load graph,
https://www.stereophile.com/images/616BW802fig1.jpg

I would look at good quality amps with big power supplies (that means heavy), that can "almost" double their wattage from 8 to 4 to 2 ohms, this is usually reserved for amps with BJT (bi-polar) output transistors.
EG: Krell, Gryphon, D'Agostino, Parasound Halo JC1's, and many others 

The 802 D3's are efficient, at tested 91db, so a even 100w amp at 8ohms is fine, so long as it "almost" doubles to 4ohms (200w) and 2ohms (400w)  

Cheers George 

Thanks for the suggestions George. I  probably shouldn’t have take this thread off topic by asking for suggestions. My bad. There are plenty of threads on that topic.  But...

I’m currently running a CA-2300 with my 802D3s (both bought used) and am very  satisfied with the combination. I will say, on very quiet passages, I can hear the air movement from the fan. This has pushed me away from the CA-M600 that was suggested.  But, the upgrade bug has hit.

With the MC611 out, there are lot of used MC601s on the market.

I’ve run the 802D3s with a very nice tube amp, 75 wpc Kt88. Sounds good, but a little loose and bloated in the bass with a very very slight glare in the upper mids. Mathematically, and to my ear, tubes and 802D3 are not the best match.  (Still on the hunt for speakers for my tube rig)

My my concern is  that  Autoformers may have a touch of that (obviously nowhere near as much as tubes...especially with 600 SS wpc!) without the magic of tubes.   

Just to get a feel for the Mac “sound” I listened to a MC452 with 802D3s in a poorly set up big box store. (The 601s we’re hooked up to Maggie’s, and they didn’t seem inclined to move them...they knew I was “window shopping) Seemed warmer, yet slightly less detailed than my 2300. Overall, I preferred my CA-2300, way better staging and presence, but that is likely more to do with the room.  

Way off topic and rambling. Probably just keep the CA-2300.