Possibly Ignorant Power Question

I don't think double the power output at 4Ω  over 8 is much of an indicator of how good an amplifier is... sure it's easier to make one that doesn't double but there's no reason why one that does would sound better.
My advice would be not to go for an amplifier that's more powerful than you actually need. Most if not all amplifiers sound better running at the top half of their rated output so if you go for something four times as powerful as you need then the cost of that unused power is a reduction in sound quality. The other thing is that most volume controls sound worse the more you turn them down as well, with the exception of decent resistor based attenuators. I did a short blog post on amplifier power vs loudness that might be interesting.

Keep in mind that a manufacturer's spec of doubling into 4 ohms is often not accurate when the amp is actually tested.  For example, the specs may say 70wpc into 8 ohms and 140wpc into 4 ohms.  The actual tests could show something like 110wpc into 8 ohms and 150 wpc into 4 ohms.  Technically, the amp exceeds its specs, but it doesn't come close to doubling into 4 ohms.  

"...It should be pretty obvious when using this speaker it is totally irrelevant if amplifier power doubles. All this stuff becomes irrelevant..."
Unless you like speakers like big Magnepans and others.   

"...Try and find the Martin Logan owner who says wow I can use any amp and my speakers sound great! No such thing..."
I'm one. The M-L Electromotion ESL is 91db efficient and I drive them very well with my 25wpc tube amp. Every rule has an exception...I do agree on your efficient speaker premise, it makes life easier for sure.  

@smrex13 I hear you but the one I really like was tested by Stereophile and exceeds both 4 and 8 ohm ratings by a decent margin.

@millercarbon I'd like to know what else you think is low impedance besides Tekton?

@oldhvymec and others....rest assured i'm not making a decision strictly off of this, it was more curiousity. Mcintosh is the example here.  The MA352 hybrid integrated is rated (from memory) @200/8 and 320/4 ohm respectively.  Yet the more expensive MA9000 is 300@any impedance.  Why not tout it as 300/8 and 600/4 or whatever it is?  It does seem to correlate to their autoformer (?)  products.  

mtbiker29 OP
So the question is why do some manufacturers then have ratings such as "200W@8,4,2 ohms

vinylzone25 posts04-10-2021 11:48pmTwo possible reasons. First is if it’s a tube amp. Most use transformers so the different taps all put out the same wattage. Second is the amp is current limited.

Mac’s also have those sort of specs because their Solid State amps have output transformers, and they can’t even come close to doubling for each halving of impedance, I’ve never like their sound.
The only I ever like of their was the original tube MC240 on Quad 57's
https://kenrockwell.com/audio/mcintosh/mc240.htm

Cheers George