Retrofit Subwoofer on High Performance w/o Subwoofer

[IMAY2023]

I've been a bit confused about the stereo configurations. It seems like there are four levels based on the config options:
Performance audio
High performance audio
Whatever the HK one was called
Whatever the B&W one was called
Mine has high performance audio. So is this not the bottom end specification, one up from the bottom as it were. Not sure if it has a sub - don't think so. So I could in principle retrofit a Volvo sub to my amp, even though it's not an HK system?

Performance Audio > no AMP direct output from IHU (4 channels only) 
High Performance Audio > with basic AMP (AUD) under passenger seat .   This one two variants with / without SUB but  without rear bench or roof speakers.  Some variants don't even have MID range on front doors and rear doors (90 series).    
High Performance Plus Audio > HK system.   Includes roof / rear bench, MID range on the front doors (90 series has MID range on rear doors too)   
Premium sound audio  > B&W > Same as HK + tweeter on the center dash and tweeter on the roof speakers or rear bench for 90 series. 

On My S60 I used B&W AUD came from s90. I added MID range on the rear doors (had to add wire from AUD to door for MID + high channels)  and also upgraded the rear bench speakers with tweeter.  


For those who upgraded to B&W speakers but kept the original trim panel on the front door. 
There is fabric on speaker grill. I removed it. Now I can see the B&W speakers just like B&W silver grill. Not only that but the sound just got better and cleaner.