One of the quirks of the RAW image format is that there can be quite a difference in the interpretation of a file, depending on the RAW converter. The same image can look quite different, depending on the software used to decode it. Aperture does a pretty good job with most RAW files, but your personal preference might be to use a different converter for certain files. For example, if you prefer the RAW conversion from your camera manufacturer's supplied software to Aperture's interpretation, you might want to use that software rather than Aperture for images from that camera. Another possibility is that you may want to use a feature that Aperture doesn't have in its conversion, such as fringing removal or color profile support. You may want to use a third-party converter to enable those functions, but you still want to keep your images in Aperture.
There are a couple of workflow possibilities that you can use to accomplish the task of using a different...