Importing AVCHD (MTS) 50 or 60 fps to iMovie 11

Hello!

Right now I'm using the a Sony Nex-5N camera but about to buy the latest 5R model. With 5N I have an option to save video either as MP4 or AVCHD (in which I can set the framerate to 50 fps). I'd like to do that because the slow motion (50%) looks good and I really want to use it.

However it seems difficult to import 50FPS MTS files to iMovie. In iMovie import from camera window these files appear gray and can not be selected for import.

I've tried several converters to convert from MTS to MOV or MP4 but they all loose quality - obvious "boxes" when put in pause for example.

Any ideas how to work with 50 or 60 fps MTS files to get them to iMovie in original quality?

thnaks!