the blue wires look like low voltage wires, possibly for speakers. the red/black one next to it looks like your cable. the box to the left of those, 2 whites/2 grays, are live 110 voltage, which looks like the 3 holes above feed from it. is it possible the outer ones could have been for lights? don't know if those would have been speaker boxes. they look more heavy duty. get a voltage tester and see if they are all live. But the simplest way to figure it out would be to get an electrician out there!

yes, those look to be connected to the media wall. your prior owner was very cognizant of his wiring! makes it good for you. but yes. if hooking up your media and sound system, you may have lucked out. just have a pro connect the wires for you.