Retrofit Volvo V60 B&W

[IMAY2023]

Retrofitting a sub to the XC90, probably the wire diagram is similar to the other Volvos

Yes, they are similar with minor differences. 
90 series have three speakers on the rear doors while 60 series have 2. 
MID + Tweeter on 90 series have its own channel from the amp (AUD) while 60 series Tweeter and Woofer are parallel on the same output channel. 
Because of this difference, the B&W AUD is also different for 60 and 90. So, pay attention to the donor car!