Autoformer vs Speaker impedance Curve

Trust your ears....there are too many variables and competing criteria in the design to try to follow. Also, recommendations from someone who designs and builds amplifiers for a living (Atmasphere) is much more credible than someone who reads specs and just spits out what they’ve read. Name starts with a "g".

@73max The amount of feedback is usually given in the spec sheet.

Bubble still up, your having illusions, or didn’t do your homework.

Really?? Your prior statement which I quoted suggested that you don't understand how feedback works. And here you are doubling down.

We make zero feedback amplifiers because of some of the problems that Nelson also points out in the article I linked. In other threads, @georgehifi , you are adamant that Nelson is the guru, but in this case you don't seem to want to acknowledge him. You can't have if both ways.

Here's a little primer on how it works with feedback- you can use little or none (which means you have to rely on other means to suppress distortion). If you use a moderate amount of feedback, Bad Things happen- its use will be a degradation. But if you use a lot of feedback (20db or more) then it use is far less audible (it can start to compensate for the distortion it introduces) and so can be pretty effective. Of course, this is the tip of the iceberg; I don't like feedback because even in high amounts it makes the amp brighter than real life (so its a coloration).  Since we make tube amps, I also want soft clipping, and feedback pretty well means that soft clipping isn't going to happen.

Here is another excellent article on some of the nuances of feedback design in an amplifier:
http://www.normankoren.com/Audio/FeedbackFidelity.html
When you are done with Part 1, read Part 2 as well. All the math and proofs are presented.

73max OP

Don’t listen to those that have anything to gain with their own product by promoting Autoformers, as they are biased and blinded because of it.

Just do the experiment for yourself, you have a great amp already (the Classe), borrow beg or steal some Autoformers and put them on your Classe and see what happens to the sound.
You will realize in first 30sec they are not good for amps that can do the job correctly without them. But that they are a band-aid fix for amps that are not correct for the job at hand, and you’d be better off just getting the right amp instead.

Also the fan noise you say you have. As I said before you make sure the filter is clean and you "could" have noisy bearings in the fan they are just like desktop computer tower fans which get nosier with age.
Another thing is to make sure the wall behind the amp if close has a sound deadening pad on it as the noise can reflect of this back into the room.

Cheers George

+1 @georgehifi
Your Classe CA-2300 amp is a perfect choice for your B&W 802 D3. If you want to upgrade, you can get the Classe CAM-300 monoblock amps or the CAM-600 monoblock amps. Just clean the fan filter.

In most ideal scenario, autoformers won't be perfect choice for your B&W 802 D3. Classe amps will be better choices for your B&W 802 D3.
I've heard the B&W 802 D3 driven by Mac MC601 monoblock amps and have compared them with the Classe CAM-300 & CAM-600 monoblock amps in the same setup, and the B&W 802 D3 sounded best driven by the Classe monoblock amps. I've also heard the B&W 802 D3 driven by your Classe CA-2300 stereo amp and it was even better than they were driven by the Mac MC601 monoblock amps. 

The Classe Omega Reference monoblock amps are phenomenal and indeed superior to all Classe Delta series amps including the CAM-600 monoblocks, which is the flagship in the Delta series amplifier line.
If you still want to purchase those Omega monoblock amps from 2004 I can only say go ahead but you will need to send them back to Classe in Canada to get them looked at, to see if the caps or anything that need replaced or serviced.

@73max  Just for the record, I've nothing to gain if you buy a Mac with an autoformer in it :) 

However, you if you can find a set of ZEROs (which, so far as I know, are the only outboard autoformers available for this task), I think its a very good idea to give them a shot if you feel like it.

One thing George is ignoring here is that in a Mac, the autoformers are inside the feedback loop, which makes a difference on how the amp behaves. As others have suggested, audition is the arbitrator.