I always prefer to use aux sends and if possible separate EQ for ancillary spaces (lobbies, overflow, cry rooms, etc.). Typically, these rooms do not get any direct sound from the live sources, which may mean they need a much different mix. They also often have very different acoustical environments and systems compared to the Sanctuary. And you may want to have a dedicated ambient mic or mix in some open mics just to give a sense of 'space' and activity from the Sanctuary to what is heard in the ancillary spaces. As a result, what is needed from the sound system in those spaces can be quite different than what is desired in the Sanctuary.
On the amp, not knowing what the CA1 replaced (although probably a good chance that it was something like a TOA, Dukane, Rauland or University product), do keep in mind that with the CA1 you have both an input level control and the Master volume, so you may need to find the combination of levels that works best (you might also want to verify that the input is set for "line" on the rear panel). However, improper connections for the outputs can cause problems so make sure that any 70V speakers are wired across COM and 70V on the main output terminal strip or across COM and one of the Zone outputs (1, 2, 3 or 4) on the Zone output terminal strip, which default to 70V operation. If you have any 4 Ohm speakers connected, they should be wired between COM and the 4 Ohm terminal on the main output terminal strip.