340 Speakers...
Mine are installed on either side of the pedestal, below the table flaps. You probably could put them in the access holes though. From the nav station you can run behind the hanging locker where there is a conduit that runs all the way to the starboard side aft locker. If you're lucky there will be a messenger line ready for you to use, if not it's a PITA but you can get through with a fish tape. From the aft locker my wires run across to the port side locker on top of the fuel and holding tanks (access by removing the aft bulkhead in the master cabin) and then through a chanel that goes to the pedestal (remove cockpit floor). I'm not sure how you'd get the wires into the arch, might need to drill a hole from below, I don't recall seeing any easy access. Have fun crawling around!