Sorry, Just tried it myself - don't know how that happened, must have changed it at some time by mistake
Easiest way to solve it open up musicbox.local or go to the ip address for the machine.
Browse down to the settings page, select the Musicbox option and halfway down page is the 'Root Password option, write a new password in there, reboot, then log in using Root and your new password
you could also go to the config/settings.ini using your pc and enter the root password almost at the bottom of the page
I have just downloaded and tried the same one as you and apart from the password situation all seems to work fine on the Pi Zero.