Are the Z's the track related pads? Most if not all track related pads will squeal badly on the road because you are simply not getting them hot enough.
With DS2500, you need to break them in properly (like proper cooking/smoking hot) to get good transfer of pad material to the disc. This will stop the squealing. However, due to the way that the pads work, this material will wear off over time if you dont get the discs hot periodically. They use 2 ways to stop the car, one is the resin which is transfered to the discs. The other is mechanical, metal filings, in the pads dig into the surface. This will wear off the resin if you do not get the discs and pads hot enough frequently enough and you will get squealing. If you bed them in again, you will get rid of it as you have a coating of the resin on there again. Hope that makes sense