Powering nine home speakers

     Okay, understood.  Then, you plan to run and listen to your music in mono, right?
     Seems like it'd be hard to perceive any of the benefits of stereo sound with 9 in-ceiling speakers.  I guess you could try by running one side of the room  as the 'left' channel and the other half or so of the speakers as 'right' channel speakers. However, I have no experience in doing this and the results are unknown to me.  For example, people would likely predominately just hear the sound from the speaker they're closest to which could be a left or right configured speaker.  So, it seems most of a scattered group of people in the room would be listening to just a right or left channel of the music and this perspective would change as they moved around within the room. 
    Off the top of my head, running all speakers in mono may be the best solution.

Tim 

Can I ask what’s the risk if the impedance doesn’t match (ie using the current speaker selector and a second amp)? Harm to the equipment or just uneven sound?

Not too many power amp can handle 2 ohms or less load, Some amp protection circuitry will lower the output or shut itself down, some will over heated and caused damage! That’s the reason for impedance protection circuitry.
If you want to use the ATM7, wire the speakers close to 8 ohms:
http://www.colomar.com/Shavano/4ps-spkr.gif

Thanks again hifiman. Currently everything is home runned back to the atm7. So each output from the atm7 connects directly to the speaker. So with nine speakers does that mean I’m somewhere around the 1-2 ohm load? I’m going to study impedance ohms now. 

Try connect 4 speakers as a group follow the wiring diagram, one group for right channel and one for left channel, leave the last speaker unconnected and see what’s the result.
http://www.colomar.com/Shavano/4ps-spkr.gif
https://www.amplifiedparts.com/tech-corner/speaker-impedance-power-handling-and-wiring
Please refer to ’Example 4’

I helped my friend wiring 8 speakers for his 2000sq ft. restaurant dinning room powered by a 80Wx2 receiver with satisfactory volume level.