Retrofitting from standard audio (no subwoofer) to HK

[IMAY2023]

Hi 
You probably don't have the roof speakers and the smal speakers in the rear door.

Just switching the speakers do a lot, you dont need to change the amp for it to work, audio will be much better

But the audio will be a lot better when changing the amp.

Just take a look at my V60 post. Should be almost the same. But for the 90 series, extra speakers in de rear doors.

https://forums.spaycetech.com/showthread.php?tid=24

It's not same S60, V60 do not have MID range speakers on the rear doors. Not only that, the wiring is also different from AUD (amplifier) to the rear doors. 
On S60 and V60, rear doors have only one channel Woofer and Tweeter are wired in parallel. 
On S90, V90, XC60 and XC90 rear doors have two channels,  Woofer and (MID + Tweeter in parallel). 
The software in the AUD is also different. If you connect and S90 AUD to S60, you won't hear anything from your tweeters.