If that quote isn’t enough to spur you to seek out a part #9452029 amp for your P80 Volvo, I don’t know what will.
This a good post with helpful photos incorporating instructions on installing a Volvo amp in a 1998 V70. The post is by MVS Volvo Forums member nathanso. His post is the most recent in a long, information-dense thread on amps, subwoofers, radios and speakers in Volvo P80 cars, which is an easy way to say 1992-2000 Volvo 850, V70, S70, XC70 and some C70 models.
Some notes on installing the Volvo 9452029 amplifier in a 1998 V70. Easy job once you know about the hidden features and have the right parts. The carpet on the transmission tunnel pulled right out from under the various trim pieces and refit just as easily. As an audiophile, I can tell you that the sonic benefit is well worth the effort. If you have never removed your front seats go on Youtube and learn how to not trigger the side airbag before proceeding!