uax to 669 conversion is actually related to export of audio samples / sounds from Unreal audio files (.uax) to .669 files. perhaps this is done or sought by game modders or anyone that wants to use game music / sounds in their music devices or audio stations.
Tools like Awave Studio are probably your best choice in this matter as standard multimedia players usually do not support this type of content.
Updated: September 26, 2023