Not much to say about this one other than that this only either counts your first or your best score on each song in your library, so you won't gain much (or anything) by replaying songs you have already played unless you add more band members.
Without any DLC and playing solo, you'll most likely have to come close to 5 stars expert on every on disc song to get this. With DLC, just play songs from your library at least once to add them to the total and you'll get this easily.