Monoprice 2-Channel A/B Speaker Selector - Black With Volume Control, Built In Independent Volume Controls, Accepts Wire Gauges Up To 14AWG

What you’re doing will “work” it’s just that surround receivers are extremely unintuitive for customers. Does the Onkyo have an App? If it does, the Zone2 controls are probably much simpler in the App than on the remote / unit. As other have said, if it’s an option you can just tie the main indoor and outdoor speakers together on the “Fronts” and then run that into a selector box with volume. Leave the surrounds and subs as they are: https://a.co/d/0iwzKZ2S And Again, yes it will work with using Zone2 it’s just confusing for dumb customers