While camera manufacturers will reuse the same filename extension (in your case PEF) across a range of there cameras the actual data in the file is different for each camera.
What this means is that the ability to decode a raw file is based on the camera it was taken in not the filename extension
You can look at OS X Mavericks: Supported digital camera RAW formats for the latest list of cameras supported by Aperture 3.5 and Mavericks
If you are really running 10.6 as your profile shows then you need to search the Apple Support site for the list for Snow Leopard. Remember SL and the version of Aperture running on it are no longer being updated to my knowledge so what cameras you have in 10.6 now is all you're likely to get.