Concerning N51 vs N52 exhuast. It's the section after the secondary cats that is different.
After checking on realoem, both engines do have secondary cats. It looks like the muffler & resonator are one part in the N51 (Rear Exhaust PN 18307572671), whereas the N52 they are two seperate parts (Center Muffler PN 18307567138 & Rear Muffler PN 18307566941). Pictures may explain better.
Here's the N52:
Here's the N51: