Yes, it's controlled from somewhere in the dome, the speakers in ride queue lines are fed from a source located near or at the ride - but can be turned off centrally at the dome or overridden (so u can basically change the CD of the stealth music to one with a different playlist on loop) - but this again can be overridden at the dome so every speaker (most) on the park can play the same thing {e.g. end of the day music} - as a side note, if the end of the day music is playing and the operator presses one of the ride announcements it will override this then revert back to the end of day theme.
Stealth, Nemesis Inferno, The Swarm, and Saw: The Ride have some form of auto start announcements (Heads back : 3,2,1 go go go starts automatically, dispatch theme on nemmy, swarm noise as train leaves & Billy puppet/jigsaw on lift) <list not exhaustive>
Each ride has its own pa control with the required tracks on it; they are in an amplifier system. Every ride console has an announcement control PA unit, which if operated will override any music playing in that ride area and play that announcement then revert to the original music. Each ride pa is divided into zones, each announcement is programmed to play in certain zones (playing the announcement that the car will start moving on saw will only play where speakers are on the brake/trim sections/station); in addition the operator can select the zones of a ride that their manual pa announcements can be heard from or they can select 'All Zones' which will be done in the event of a shutdown - also, pressing the pre - recorded shutdown announcements will play in all zones.
This is what the PA boxes look like (yes it's from AT, but they are pretty much the same)
http://old.towerstimes.co.uk/history/behind/rita%20(7).jpg
Edit: Here's the panel from rush - they all look like that.
http://i241.photobucket.com/albums/ff31/NEILFEVER78/Rush200876copy.jpg
