The Arc is designed to replace your receiver, by connecting to the TV’s ARC output.

If you’re using your receiver as an input switch, just use a different HDMI port to connect it. 

Note: You’re not going to be able to sync both the receiver’s speakers, and the Sonos speakers. Sonos isn’t designed to allow third party speakers in their Home Theater paradigm, so no “surround speakers” connected to the Pioneer, as one example.