As some of you may know, there's a cheat screen within the options menu of GH3. I would suggest people beat the game at least once through in order to do the boss battles and see the cut scenes, as this unlocks the songs only within Quickplay menu.
CHEAT CODE: YO, RB, RO, GB, RY, YO, RY, RB, GY, GY, YB, YB, YO, YO, YB, Y, R, RY, R, Y, O
How do I use this code?
Go to the cheat menu within the options menu of GH3. Once there, you'll see the neck of the GH guitar, where the buttons are located. All you have to do is play the pattern of notes like you would a regular song.
So for the first three notes you would first hold down the YELLOW and ORANGE keys, and then strum the note. You would then hold down the RED and BLUE keys, and then strum the note. Next you hold down RED and ORANGE, strum, etc. There is no time limit as far as I could tell, so you can take your time. You will see a message stating that all songs have been unlocked if you're successful.
!REMINDER: THE SONGS WILL BE UNLOCKED IN THE QUICKPLAY MENU, AND NOT THE REGULAR CAREER MODE.!
Why would I want to use this code?
There are actually six more songs that you won't be able to access, UNLESS you can play co-op mode. These songs - although listed for co-op play - have just as much button pressing as the other, regular songs. Which is why I don't understand why they aren't unlockable during career mode. I'm sure there's a reason though.
A couple of the co-op songs are, Sabotage by Beastie Boys, and Suck My Kiss by RHCP. Needless to say, those are the two "new" ones that I've been playing out of six.