IFF - Audio Interchange File Format. Audio Interchange File Format (or AIFF) is a file format for storing digital audio (waveform) data. It supports a variety of bit resolutions, sample rates, and channels of audio. This format is very popular upon Apple platforms, and is widely used in professional programs that process digital audio waveforms.
Shockwave Audio (SWA) is MPEG 1 layer 3 audio with some extra info on the header of it. I have managed to import MPEG audio into Director 6 as a SWA file. I've had varying degrees of success though. It would appear that some of the time director can't read the header data from the MPEG file so it can't play it back. But 80% of the time MPEG is treated as SWA. The trick is to change the file type (on the Mac) from "MP3!" to "SwaT" or rename the file suffix from .mpg to .swa (on the PC)