Filename extensions being hidden (as in the Finder's "Hide Extensions") should not interfere with copying and/or moving the files to a PC.
The extensions are hidden -- not non-existant. The ability to show or hide extensions has nothing to do with whether or not the file actually has an extension, and, if files are copied to a PC while the Mac OS X's Finder is set to "hide extensions," those files will be copied over (and have all their respective extensions) the same as if the Finder was set to "show extensions."
It's only a preference -- it doesn't affect the actual file nor its extension in any way.
But yeah -- if those files never had an extension (which isn't the same as a "hidden extension"), then a batch re-namer to add ".AIFF" to the end is the best route. Automator has been mentioned, and it's quick and free. If you're looking into more powerful renaming capabilities (those which can come with managing a historic library of music files, for example), I highly recommend "A Better Finder Rename" (available with a simple Google search).