Awesome hack! Tried it on my MZ-R500 and was delighted to discover all those new features.
One question though: is there any way to change the equaliser settings besides using the maintenance-mode? I think that the sound quality using the two prefixed settings (SOUND1 and SOUND2) are an improvement over the BASS-settings but it would be really great if I could adjust those settings too. Since the R500 doesn't support the remote I would guess that these settings would have to be accessible via some kind of key-combination.