You can toggle between the music at the site via the controls in the upper left of the page. There are currently two songs, but more will be added in future updates.
Unfortunately, there aren't any actual images of the bonuses at present, but at least we know they're on the way! The retail bonuses are in addition to the hard cover Grand Knights Chronicle visual book that everyone will get.
[end_p text="Continue reading for the latest screens" /]