I did not know that 2018 S/V 90 did not offer HK option. Since you want to upgrade to HK, you will need the enclosed diagram for the later models. The wiring for HK and BW are the same for the same model from 2019 to 2023. But as I mentioned the amount of speakers (wiring) and AUD outputs are different between (90 and 60) series.
In any case, you will need to rewire one way or another. So, I recommend upgrade to B&W AUD.
There are some minor changes like the 3rd channels on each front door and second channel for dash speaker with B&W amp for MY24+. So, get the amp from 2019 to 2023 if you decide to go with B&W.
Before you decide, just pull out the door trim and check what is your current wiring, and if you have the places for the MID range speakers on your trim panels. (you will need them if you upgrade the AUD regardless of the year and type).
In any case, you will need to rewire one way or another. So, I recommend upgrade to B&W AUD.
There are some minor changes like the 3rd channels on each front door and second channel for dash speaker with B&W amp for MY24+. So, get the amp from 2019 to 2023 if you decide to go with B&W.
Before you decide, just pull out the door trim and check what is your current wiring, and if you have the places for the MID range speakers on your trim panels. (you will need them if you upgrade the AUD regardless of the year and type).