Our 525iT had the extra pair of forward facing speakers (but no sunroof). I considered modifying the rear headliner but couldn't find the exact trim pieces needed in the ETK to support 4 speakers in the rear.

Considering how infrequently I'll be in the second row, and my desire not to alter the interior much (I guess I'm not confident) from stock, and the advice I recieved here, I put my money and effort into the front speakers and just put coaxials in the rear for fill.