How many ceiling speakers can I connect to an Amp

You can hook six Sonos/Sonance speakers to each amp, only four other brand ones.

Just to clarify, I believe the Sonance models need to be the Architectural series, not any Sonance speakers. 

Did you read the instructions? https://support.sonos.com/en-us/article/set-up-your-sonos-amp

Note that in the case of non-Sonos/Sonance speakers, they need to be 8 Ohms each in order to connect two pairs.  You can only connect a single pair of 4 Ohm speakers.