Powering nine home speakers


Hi. I have a large open living room and want to increase the wattage I have running my speakers. I currently have an Onkyo 7-channel amp and took the front left and right outs and have them going to an OSD Audio ATM7 7-zone speaker selector. However the Onkyo amp is not powerful enough to drive all 9 speakers strong enough. It sounds very weak. 

The only device I want to connect is a sonos connect that I have. Currently I connect the optical out of that to the Onkyo amp. Should I introduce a second amp? How exactly would I connect them? Would I run the sonos connect into one amp and take the preamp outs to the other amp? Can you have a standard front left and right out AND a preamp out at the same time?

i only want/need stereo sound not surround. 

Thanks!
jj91709
Your parents raised your parents raised a considerate and compassionate son Tim. They should be proud. 
Hifiman, can I ask how you would recommend wiring the 9th speaker? It seems like I could run 3 in parallel which would be 2.66 ohm. My onkyo amp specs are 8/4/3 ohm. Is the difference significant enough?

i also just received a second amp that is 100w x 2 (Yamaha R-S202) which is 8 ohm.

I would prefer to keep them in stereo as the layout of the room works well even with the odd speaker due to the seating. 
Since you have the onkyo receiver with 7 channel of power amp, and a stereo amp (Yamaha R-S202), why not make full use of all 9 channel of amplification!
Just connect 7 of the ceiling speakers to the onkyo speaker terminals via a/b speaker switcher on each speaker:
https://www.gearslutz.com/board/attachments/newbie-audio-engineering-production-question-zone/421582...

connect the Yamaha line in to onkyo front R/L out, and use the Yamaha to power two more ceiling speakers.

Select Full mono or Neo 6 music playback mode on your onkyo for room filling music listening.
Great idea! How’d I miss that? ;)

What is the point of the switch in this case? I’ll always want all 9 playing at the same time so is a switch necessary?
I thought you have a HT setup using the onkyo in a dedicated theater room and want to switch the music to your living room?