Since my last post on this thread, I've been looking at the
Eisenmann sport muffler as an alternative to the BMW PE. See my post
here. These are some links to videos of these fitted to the 325i:
BMW Performance Exhaust 325i E92 (N52B25)
Eisenmann Sport Muffler 325i E92 (N52B25)
As for pricing, I found an online UK seller,
Prestige performance centre