If you’re not using the Sonance speakers, than you can only connect 2 pairs of 8 ohm speakers.  I would recommend first going with the Sonance speakers and see if that fills the need without additional speakers.   If you do need more, than you can get an impedence matching speaker switch between your speakers and the Sonance/Bose speakers.

Some additional points.  It’s generally not a good idea to mix speaker brands as they tend to have a signature to them. So perhaps you might want to go with all Sonance or all Bose.  You can buy from Sonance direct at Sonance.com

One other point, I didn’t want to mount speakers under the eaves at my own home as I didn’t want audio pointed at the neighbors yard, or drown out conversations.  I also didn’t want to go with on ground speakers, so I ended up mounting speakers on fence posts I put up a few feet behind the pool.  Pretty happy with how it turned out.  Now, a couple years later, the landscaping has grown up around them and they are not seen for the most part.

You don’t want low Ohms, you want high Ohms (8 is the bare minimum for 2 pairs). 

Impedance is calculated like this:

So at 4-8 Ohms, you will be lucky to get two pairs on there.  Maximum load for the Amp is 4 Ohms. Two pairs of 4 Ohm speakers is 2 Ohms, so two pairs of 4-8 Ohm speakers is 2-4 Ohms. 

Thanks guys.  I am going to try it out with both sets of the Sonos speakers and see how it goes.  I do have 2 Sonos moves which I can use near the pool so I will just do that for now.