personally i found that i got a HUGE upgrade from changing to a JVC sh99 head unit. It has super advanced burr brown 1702 24 bit convertors. Anyway being a audiophile at home i think the sound i get in my car now is pretty decent, for regular speakers. Stock 850. If you reall want to go insane you could get the dynaudio upgrade that was documented. however that is about a 1500 dollar investment. I really have to say its totally not worth putting the s80 speakers in your 70. If you want to keep your volvo head unit you could look into getting some mcintosh car amps for the volvo HU. The volvo amps are really reasonably depressing even the "premium" if you read the specs you will find a reasonably high distortion level.