Yep, I'll second Dave's recommendation to switch to DNG. It is far more future-proof and allows you to access images from almost any native Mac application. I use Aperture as well and it works flawlessly. Kudos to Pentax for offering DNG, it's a much more flexible format than a proprietary RAW format.
Oh, by the way, you should be able to convert any of your current Pentax PEF format to DNG using
Adobe's DNG Converter application (DNG Converter 5.4 or later will do the trick).