(sorry for posting so much) there's a second voice near the end of the Link one, more high pitched like...
Mario? somthing close to that, but why would Mario sing about Link?
ok the first easter egg you can get is at the dice level,look to the rightand click THE CAKE IS A LIE. the next is at the end. click the dot on the ! and get the second song ( which sounds like a CD-I song)