Are all iPad equalizer apps restricted to a fraction of songs in the Music App Library?

Im looking for a good equalizer app for the iPad. I’ve tried some. Like Boom, but they only access a fraction of my songs in the iPad Music App Library. I understand that this is due to licensing and copyrighting. I’m therefore assuming that all other equalizer apps also do not have access to every song. Is this true? Are there any apps that have access to all songs? Or is this strictly forbidden?

[Re-Titled by Moderator]

Original Title: Equalizer app