The preamp has two functions:
1) It provides the correct voltage to polarize the CA-11s. The mics require 9V to be properly polarized. The plug-in power of the M10 supplies 3V which appears to be enough voltage for the CA-11s to be functional in your recording situations, but to have the mics operating at their specs, they need 9V.
2) It supplies gain. Whether you prefer the M10 amp or the Church amp is up to you (ie., you can set the Church gain at 0, and do all the gain on the M10, or set the Church at the optimal gain). Many here (including myself) think the Church preamp provides clean, nice sounding gain. I've heard very good things about the M10, but I haven't seen any comparisons.
So bottom line is that to operate the mics at spec, you need to supply them with 9V from the preamp. If you want to reduce the bulk, it sounds like you can use a battery box to provide the correct voltage and get all the gain from the M10.
Warning...relative newb here...
So I got a church audio preamp with my mics recently...just to be safe....and I've recorded probably 20 shows now without the preamp and never had a problem with just running the mics straight into the deck (and one of the shows was mind-bogglingly loud). Can someone tell me why/where/when I might need this preamp? I'm mostly recording rock music in clubs and occasionally stadiums/amphitheaters with church audio 11 mics and a sony pcm m10. Thanks in advance for any help you can offer!