Thought I'd share a few things I've been looking into. Info applies to V90cc, but may apply to other models as well.
In 2018 and 2019 Volvo offered a Base (2??w, 10 speaker, code K502) stereo, a premium Harman Kardon (650w, 14 speaker, code K504) stereo, and a premium Bowers & Wilkins (1400w, 19 speaker stereo, code K503). However on 2019 Volvo Ocean Race models, the starting stereo offering was the HK stereo, which you could option up to the B&W stereo.
In 2020 Volvo did away entirely with the Base option and the HK stereo became the new standard option on US-spec V90cc.
My assumption was that Volvo saw that very few US destined V90ccs were being bought with the Base 10 speaker stereo, and that starting in 2020, with only the T6 being available, even fewer would be opting for a stripped down stereo option. I had a suspicion that Volvo also made this move because the HK and B&W systems share wiring harnesses, and it would cut down on inventory and assembly line logistics. I based this on that the missing 5 speakers from the HK system are; the nautilus speaker on the dash (the other center dash speaker is present on the HK system), the tweeters back in the headliner (the other midrange speakers are present on the HK system), and the mid-range speakers in the rear doors.
From an older look at the Base vs. B&W system on the XC90:
And the wiring present at the amp on a V90cc with the HK system:
Notice that the wiring for the V90cc with HK is identical to the XC90 with B&W.
As of now, all that means is that the wiring to and from the amp is identical. Having seen B&W headliner speakers, I know those are drop in replacements with the HK units. I also know the center dash B&W speaker connector is the same as the HK speaker. So for those, there shouldn't be an issue swapping them in. The only question is whether the rear door harnesses and connectors are the same, to accommodate the B&W mid-range. The parts fiche isn't much help here, as they're a mess of several different options and production change overs. So, TBD on that.
Anyway, figured I would share for those that are interested.