Just out in a very simple outdoor audio addition to a sonos system. Added a Sonos connect amp and two russound rock speakers. Just happened to be for my sister. When done she asks if they can add "one more speaker" to the yard at a later date.
I know that sonos connect amps are stable to 4 ohm. Done quite a few without incident. I always avoided a "lopsided" connection (on all amps)... One where one channel sees 8ohm, and the other sees 4ohm. I know there are all kinds of gizmos like mono mixers and summing vc's that can be used.
Any harm in simply loading the amp lopsided.
I'm Not an engineer, but I play one on TV. My handle is Tweety but I have nothing to do with the organization of similar name. I just had a really big head as a child so folks called me tweety bird.