Taperwire. Invisible speaker cable. Unroll it onto the walls like sticky tape, and paint over as necessary. From $22.50. Wonder whether it degrades the sound quality enough to notice?
No drilling necessary. Just press Taperwire on the wall and attach your speakers and sound system. Hidden by paint, wallpaper or spackle, this paper-thin wire will go unnoticed. You can even lay it under carpets—no bulges!