Oddly, the 2-piston brakes used on many of the Volvo's are used as upgrade for 944's (as a step between full on turbo brakes and stock single pin jobbies)
You need more braking power, right? Why would you then remove surface area of the disc and potentially end up with cracked rotors?
Good quality rotor, with perhaps some slotting to reduce pad glazing.
Stainless lines to improve pedal feel and more direct action.
Highest DOT spec brake fluid that isn't slicone based. Flush the system quite wheel and ensure there are no air bubbles.
Good quality street-style brake pad compounds as you want them to heat up quickly and work right away.
If you find that you're overheating your brake fluid then look at improving cooling or moving to a more race-oriented pad.
If you find the brakes gaze easily because they are not getting warm enough, drop back a step in pad compound.
Either way, ensure you follow proper brake pad bed-in procedures to ensure good bonding and coating of the pad material to the rotors.