Has anyone installed aftermarket graphite/metallic pads on their A4? Is the braking better and is there less of the dreaded brake dust and squeal? Are there other sources besides TAP ($125 front/$90 rear)? Can you use the pads with slighlty worn rotors or do the rotors always need to be re-surfaced? Also, who makes the best replacement panel air filter (K&N, Jamex, abt)???