You just have to change the real time play back setting in FCP. there is a button right above the timeline with some settings you can select. I think it says like "RT" or something. It is on the upper left side of the timeline window. Don't have FCP in front of me, but I do know it plays back unrendered stuff just like premiere does.
Oh yeah I know that but fcp allows you with one click of a button to unlink every video clip's audio in the entire timeline not just the one that you selected.
