It is not "iMotion", just "Motion". Export as a full resolution Quicktime file. Import that into Motion. Be sure the Motion project is the same specs as the QT clip you're going to import. I.E. do not create an HD 1080 Motion project and use standard def clips. That will blow up the SD clips to fit the much larger 1080 frame size and ruin the SD clip's image quality. Can't blow stuff up too large.
So what format are you editing in iMovie, and what format are you setting up your Motion project for?
Ok. I edit in 1280x720 and set up the project in Motion to that too. I guess Quicktime just compresses videos so much that they lose the sharpness. But I tried importing raw video to Motion and then if I can figure out how to cut the video in Motion I will get better stuff, I hope. Maybe just better buy FCproX...
There are also Render settings that can effect how clear the video appears in the Canvas. This is not how the video will appear upon export. There is no image loss when you bring a video into Motion or FCP X properly. No quality loss at all.
Motion is not an editing application, and will not let you edit video very well. Wrong tool for the job. FCP X will get you through editing much faster and easier. Motion is for grahics and effects only.