Continuation of the Sound System Upgrade - now on revision 4 or 5 - can't remember.
Re-Installed HAT Legatia Pro L1 R2 Tweet in factory vent location. First one DOA - warranty process was quick and painless.

Re-Ran Alpine Audyssey MultEQ XT Pro AGAIN
My Build evolution in current state
Phoenix Gold Xenon X100.4 @ 100 wpc feeding front soundstage
HAT Clarus 6.5" Mids crossed @ 80Hz mounted in 12Velectronics birch door baffles factory location.
HAT Legatia Pro L1 R2 tweets crossed @ 4.2kHz - mounted in factory vent tweeter opening.
USA AMPS US-150 bridged @ 450 watts into 2 ohms feeding
JL Audio prowedge single sealed 10W6v2 for some bass reinforcement.
Time alignment and equalisation provided by Alpine PXE-H660 and Audyssey MultEQ XT Pro
Sounds a wee bit better than the stock DSP system.
As with most things - this was inexpensive, nor quick to install.
As another few hours are spent tinkering with the M5 I hear another of the Wife's common M5 related comments:
"I understand my position in this relationship is #2. I'm FINE with that"

- You know when they say FINE, they really don't mean it in the literal sense.
How many of us are in the same boat?