Awesome sound but won’t play all my songs – Equalizer Review

Love the sound and the interface. But it won’t play at least a third of my 1000+ songs. It says they need to be downloaded - which they already are - or that they might be DRM. Why would they be DRM if I bought them from i-tunes to use on this phone? I’m confused. Please help.
Review by Both Sides of the Trek on Equalizer.