So where did I end up? After years of cars that were functional and with ICE systems so poor I didn't bother using them, I'm now the proud owner of a 2021 Jaguar I-Pace fitted with the Meridian Surround system.
It's a brilliant car in every way. Quiet, refined, powerful. Utterly sublime for getting around.
Being an EV, and especially a Jaaaag, that quietness really lends itself to listening to music without it needing to be loud.
But it's the M sound system that really makes it enjoyable. Sure, it's not perfect, but it's about the best I've ever heard.
For me, it needs the fader set forward, about halfway between middle and front to make a good soundstage, otherwise it sounds too indistinct, too much from behind and the rear door speakers.
The centre speaker helps imaging and it's pretty good! You don't get a feeling that the sound is coming from the door card next to you.
A touch less treble and a touch more on the subwoofer control helps it sound balanced on the move.
A few tweaks in the upper midrange for my own personal taste and a 7db cut in the 60hz area applied to all the lossless tracks on my USB stick and the final result is... nearly as good as at home!
Honestly, this is the closest I've got to the 5k experience in a car.
It could use a beefier subwoofer, it seems to roll off below 30hz.
It also does that thing that M DSPs do, which is sound good at any volume. It doesn't need to be played loud to be enjoyable and doesn't descend into harshness if you do want it a bit louder.
I can't say I can hear much difference between the Meridian Trifield and Trifield Surround modes but overall it's got the edge over stereo mode, unless you use the fader in the centre position and then I think stereo sounds better.
Since selling the Jag XF, I've stopped having music on in any car I've owned since because it was just too unpleasant.
I find myself putting music on again. And it's wonderful.
Frequency response measured in case anyone is interested:
6 measurements taken around the driver's headrest and averaged. M surround mode, fader set forward 4 clicks, treble -3, bass 0, subwoofer +4