Weirdness, solved.
I've been having some real problems with my, frankly quite simple, system.
The frequency range coverage has been all over the place. My analysis tools that I use to get my studio monitoring system as flat as a pancake literally went into meltdown. A +6dB hump between 79Hz and 119Hz, and then a massive dip, and then a +3dB hump from 200Hz-ish to 300Hz. And then wobbles all over the shop making voices cloudy, treble harsh, and general, audible instability creating a cacophony of rubbish.
Analysis and parametric EQing helped flatten things out, but it was like sticking a plaster over it. Semi-solved, but not really a satisfactory answer and the system still sounded terrible.
I spent literally hours moving the speakers, analysing, applying curves (my lounge system DAC is actually a studio DAC, so has all the adjustments one would ever need), listening, moving, curving, listening, moving, curving. Better, but better junk.
Resigned to the fact that my room and system didn't work well together, I gave up and decided to just not listen. I blamed the speakers, the room, the amp, the rug, the dogs, the weather and anything else I could think of.
And then it dawned on me. When I set the system up originally I used my Van Damme 4.00mm tour grade speaker cables that I had in my box of Hi-Fi plethora. Really good cables, and extremely low impedance at 0.00045Ω per metre. They were a bit short so I decided to order the Van Damme 4.00mm domestic cables, which are prettier. When I thought about 'when the problem started', I realised it was after the new cables went in.
In the loft I went, found the tour grade cables, and swapped them over. Before doing any listening, I went into the DAC's ferociously deep and complex menu, and zeroed absolutely everything - flat as a pancake, as it should be.
Started playing something - and bang! Perfecto. Clean, even and crisp; like a good pizza.
Now, I don't care why two near-identical cables from the same manufacturer should be so electrically different (the tour grade is a few thick strands, the domestic a very multi-strand), but the difference is staggering.
So the thing to take away from this post is... anything can be the cause of the problem, and don't discount something because you imagine it should make no difference.
I've used the 4.00mm domestic cable in many systems and never had a single issue, but in this system it was a stinker.
Lounge:
Samsung QE65QN80F 65" QLED TV
Echo Link streamer
RME Audio ADI-2 FS (AK4493) DAC
XMOS DSD Async
Emotiva A2+ power amplifier
Neat Motive SX1 speakers
Van Damme 4.00mm tour grade speaker cable
Nakamichi Fanlock banana plugs
Chord Clearway XLR interconnects
Audioquest Crimson USB interconnect
QED Quartz Reference optical interconnect
Studio:
2022 MacBook Pro 14" M1 Pro 10/16/16/16
SMSL DAC
Modified Fosi P4 preamp
Adam Audio T5Vs
Fenton 10" active sub
Roxel RBS 300s
Several valve preamps