Ahhhhhh there is a cable run already have a looky it might be shockingly easy to run cables next to the cables going to the projector as in pull the cabls and see if they move.

this does show the most important rule of running cables if you think you might need any cable what so ever at any point in the futre run it when you start. example my car has a set of cables for a sub running from empeg to boot, may never be used but they are there if i need them

Option 2 however is instead of hiding speakers buy a damn sexy pair of floor standers and stick them in the corners of the room but not against the wall bass reflex etc. then the speakers are a feature not something hidden