The old OS 9/Classic freeware app SoundAppPPC will convert lots of file formats to lots of other file formats. From the Read Me:
"SoundApp can play and convert from the following sound formats:
• SoundCap (including Huffman-compressed) and Studio Session Instruments
• SoundEdit (including stereo, MACE-3 and MACE-6),
• AIFF and AIFF-C (8-, 16-, 24- and 32-bit, MACE-3, MACE-6, IMA 4:1, µ-law and QuickTime codecs),
• System 7 sound and 'snd ' resource (including MACE-3, MACE-6, IMA 4:1 and µ-law),
• QuickTime MooV (soundtracks only, including MIDI movies),
• Sun Audio .au and NeXT .snd (including µ-law, a-law, 8-, 16-, 24- and 32-bit linear, 32- and 64-bit floating point, G.721 ADPCM and G.723 ADPCM),
• Windows WAVE (including GSM-, IMA- and MS ADPCM-compressed, µ-law and a-law, 8-, 16- and 32-bit linear),
• MPEG audio (layers I, II and III, requires a PowerPC processor for playback),
• Iomega RecordIt,
• CD audio,
• Sound Blaster VOC,
• Atari AVR (including stereo and 8- and 16-bit),
• Many varieties of MODs, ScreamTracker 3 (S3M), Multitracker (MTM),
• Impulse Tracker (IT) (requires a PowerPC processor),
• MIDI (type 0, 1 and 2, including GS and XG; playback only),
• Amiga IFF/8SVX (including stereo and compressed),
• Sound Designer and Sound Designer II (including split stereo),
• IRCAM (8- and 16-bit linear and 32-bit floating point), and
• Ensoniq PARIS,
• Psion Series 3 and EPOC 32 (Psion Series 5) sounds."
You should know that SoundAppPPC generates .aif file extensions. OS X wants .aiff extensions. You might have to add the extra 'f' by hand. SoundAppPPC runs, or at least ran, in Classic as well as OS 9. There might be an OS X native sound converter out there.