I may be talking complete BS on this one, so if anyone reads this & agrees then please correct me.
I've read, and heard, in the past that Eibach DO make the springs for Prodrive, but unlike the springs that Eibach make & sell to other distributors the spec is slightly different for the prodrive ones. I've also heard reports of people having the eibach springs fitted to their cars and then having a knocking noise, possibly because the spring isn't sitting in the cups at the top of the front suspension properly.
As I say, might be total jobbies.