Make sure that in fact your front brakes are not doing all the work when stopping. I had that problem and realized that my rear brakes were not getting too hot after use. I had it checked by a mechanic and he told me that it was normal. When the car went for a final service before the warranty expired, I had to beg to Volvo that rear brakes should get hotter than they were. They changed the spring kit on both rear calipers. They charged $22.00 CAN for the new kit but they swallowed the labor. The rear rotors now get reasonably hot and I notice considerably less brake dust on the front wheels. There was no change in pedal feel after the repair, so you may not even realize if the rear brakes are not putting out their full potential.
Ari
98 S70

You could try using the aftermarket dustless pads in place of what you have now. The general opinion of the contributors to this board is to live with the dust of the OEM pads as the replacements seem to cause other problems such as rotor wear etc.
John Scales (850R 1996)