Keep in mind that the purpose of Class A isn't so any problem with the wiring can be repaired in a timely manner; the purpose of Class A is to keep the system working once the fire hits and starts to degrade the system - or at least before wiring problems can be repaired.
The feed part of the circuit gets the signal to all the devices in a daisy chain, and the return should be run as a redundant Class B wiring path so that cutting one conduit doesn't prevent devices from being activated by the panel.
As far as running more than one NAC (Notification Appliance Circuit) in a conduit, whether it's a homerun conduit to the panel or conduit somewhere out in another part of the building, as long as the feed and return of the Class A are separated to prevent both from being destroyed at the same time, as many feed NACs or return NACs as needed can be run in the same conduit. (Of course, keep within National Electrical Code [NEC] conduit fill guidelines.)
The biggest concern is survivability of the NAC. Keep the feed and return separate, and the rest can be just standard wiring practices.
Douglas Krantz
