Now that Warner Home Video has distributed the replacement discs for Superman: The Movie-Special Edition, Disc 1, there has been some web chatter about the new discs still having the 2001 audio rather than the original, 1978 audio.
The Superman: The Movie-Special Edition, Disc 1 replacement defaults to the 2001 Dolby 5.1 sound. From the menu, choose Languages and then English (not English 5.1) in order to hear the 1978 sound.
While the menu choice to hear the original audio may not exactly be obvious, it is there now. As noted before, I compared the audio on my replacement disc with the samples over at Superman Cinema and it definitely matches the 1978 version when you follow the steps outlined above.