Welcome to the forum!
Just to double check: On the Pioneer, did you set the "ARC" setting to "On" as shown on page 33 of the owner's manual?
On the Vizio, did you turn the TV speakers off? That's shown on page 20 of the owner's manual. I don't know if that's required, but it might be. On some TVs, only some of the HDMI ports support ARC, so I checked the manual to look into that on your Vizio. It doesn't discuss ARC anywhere. I find it odd that, even though the Amazon page for that Vizio discusses ARC, the Vizio product page and manual do not (that I see) discuss it at all.