Well, the pyramid would explain why the Portrait of Ruin boss music (Piercing Silence) is in there, along with the pyramid music. Just go into the options menu, into the sound section, and you can play all the music there.
Though, the fact that it's already in there leads me to believe that the dlc, at least that level itself, is already in the game...
90% of all DLC is already included on the game. We just end up downloading an unlock code. One of the images the TC showed featured the characters and level file size in MB not KB meaning they're not hidden away in the actual game.
...Wait can "on-disc" even apply to a Live arcade game?
"I'm Commander Shepard and this is my favorite store on the Citadel." Nothing says Paragon like selling yourself to every company