I have been having the same problem in FCP 6. I am trying to export audio from the timeline as an aiff file but it keeps coming out as a aifc.
I go to Export-Quicktime conversion choose AIFF but it comes out AIFC, then I tried going to Export-Send to AIFF’s and that comes out as AIFC as well. I have check all the settings I have also tried exporting it from Quicktime but still get the same AIFC file.
I have never had this problem before…did something happen in an update?