I ran HPS pads on the street for a while last year, and they work fine on this car. Are you sure ABS is engaging? Could you just be feeling pedal pulsation from a bad lathe job on the those rotors that left them with an uneven surface? (it happens). It's better to do rotors and pads separate (install and bed new pads on existing good rotors. install and bed new rotors with existing good pads), less variables to work with for sorting out problems, and the bedding process is easier in both cases, although when swapping pads you should try to scour the material from the old pads off of the old rotors first (lightly sand it off, I'd recommend ~180 grit garnet paper, and use a
flex hone to score a pattern into whatever remains).