After stage 2, you will have a folder of m4v files.
Have you tried MPEG Streamclip to convert these files?? I think if you have a fast Mac, you can import these m4v files straight into iMovie and if you don't ask for 'Optimization', I thought that it doesn't convert, but does require a lot of processing power to edit.
MPEG Streamclip can take the M4V files and convert them into pretty much anything. I use it to take my 1080p50 files and turn them into 720p25 or 720p50 AIC files. Whilst I accept that there is a tiny loss of quality, it is almost imperceptible and can be used by iMovie as high quality movie. iMovie 11 will also import them at the full 50 fps frme rate