Might be worth looking at an oem hk retrofit...
There are kits available on AliExpress but they are pricey, the install shouldn’t be too bad, but there may be a fair bit of dismantling involved, particularly the door panels , speakers and associated wiring, but having said that, once started it may not be that bad, I once retrofitted HID headlights with AFS to one of my Mk6 GTIs, I fitted everything exactly as would have been done in factory, it was a big job, but not too difficult, I think the HK install would probably be similar in terms of difficulty levels, although the kit on AliExpress has the rear tweeters, they would need fitting in to the rear doors, this may be difficult, so new rear door panels with the tweeter grills already in them may be needed in order to make life easier, for a competent installer/DIYer it could actually be a relatively easy and satisfying upgrade, it would then just need OBD11 or VCDS to code it.
VW Golf 8 Harman Kardon Full Kit Car Audio Upgrade - Premium Sound System Installation Bundle
https://a.aliexpress.com/_EQoi4vQ
