Thanks mharv. I've been following a few threads on other BMW forums and they reach the same conclusion with aftermarket installations (I think I've seen some of your posts as on my travels as well ). The ZT has "an" amplifier in the C pillar and the aerial is built into the rear windscreen but I can't see much info on what the aerial amp is. I need to do a little more digging around.

I went for a drive today and got lots of Freeview channels all crystal clear in some areas of my home town so I believe only minimal boosting will be required to get a stable and constant picture.