Call a different installer - a quality installer will liekly cut a hole at the base of your wall into the drywall, then drill a hole down into the garage. Depending on which way your joists run, this is where things get tricky. Sure, the wire may go across the ceiling in one direction fine, but the other direction, it's gotta run through some joists, which means more drywall cuts. The less drywall that is cut, the more difficult the wire run is. Drywall in your garage is also what will be cut.
When it goes up, the same scenario should happen. A hole at the base of the wall, then a hole is drilled into your garage, then wire is fished up the wall to where you want the speakers.
This may be a full one day job to get it done right: 8 hours @ 60 bucks an hour is easily 500 bucks. Then you will still have drywall that will need to be repaired and painted.