How about looking into speakers designed to be put up against the back wall, at least really close to it?
I could mention Sjøfn Hifi's QM10's. They are designed to sit bang up against the back wall, and they have a sound that is like Mcullinan wants out of his speakers, I think. They are not pretty... but they will do bass also like an angry bullfrog. And have a full and "big" quality to the music.
I believe the do not have a very deep soundstage, if that is required, and a more front row "seating" in the way they present
music but they are warm and dynamic like ... well nothing else with a 4" bass driver...

The reason for mentioning them is that they have a listening distance "Span" that is from 1 to 4 meters triangle-wise.
They should indeed at least fit this room facing any direction.
And... they have a blue led that tells you when they are close to clipping from the amplifiers input being higher than comfort..
Yup, a blue led will light up when you push them to hard.

Unusual for sure!! But then you are flexing the walls so...
Yeah, and they will have a massively large uniform sweetspot.
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I don't think they are as microdynamic as a pair of Merlins, few speakers are really...
BAM? Balanced BAM? I'd spring for a BAM! Pushing this here, but seriously man, consider it!!!
QM10's can also be active I think.
Now... Active monitors wouldn't be bad either come to think of it. Could ease the use of room tunes or digital correcting or say a TACT
or a Thiel sub integrator or what have you, a Rives PARC maybe? But NOT to forget the acoustics either, these things Don't do wonders, you NEED to also use physical dampening objects in a room to ensure perfect performance.
Just getting a digital/"trick" - bandaid, won't fix it all!
Tone/Stereomojo has tested 'Salagar speakers I believe to good measure.
You have ATC active speakers and even Harbeth active models also.
(Mhm... I've got a caffeine high here and the keyboard is taking the wrap...

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Others in this thread have mentioned active, separate amps and so on.
I have to say, that is exciting stuff! With possibilities to really "build" a perfect fit into a package or what you call it.
Imperial