Don’t use Sorenson! That’s a delivery codec, which is too compressed if you are going to Avid. The best option would be Animation codec at best setting 1280 x 720. You won’t need to deinterlace since you shot it in progressive. Keep in mind this will be a huge file if the clip is very long. Google the Sheer Video codec, it’s great for what you need. If the Avid is on a Mac, you might be able to use the DVCProHD codec and import that into Avid.
Also, if Avid can capture DVCProHD, why not try sending it out firewire from the FCP timeline to a DVCProHD tape and then capture in Avid?