The easiest thing to do is to grab both (+) signals and use that for your (+) input on the amp and then do the same for (-). So yes, tap A15-A18.
The Kicker Key amps do have auto turn on function, so no need for a remote wire.
Don't know about any ANC mics, not sure why you would need to disable them if there are. Are you concerned about ANC cutting the signal to your new sub?