Ok, I believe. Now some help with what's next?

I got a Sonos Arc Ultra and the difference the AI center channel upgrade made is a game changer for my mom and I (I have military-related hearing loss, she's 80 and uses hearing aids). I'm a believer at this point, and I'm considering jumping in with subs and 300s and all that. Here's the rub --

Also in the living room I have:

A PC
A Blu-Ray player
An Xbox Series X
A PlayStation 5
A Nintendo Switch 2
An NVIDIA Shield connected to a NAS

Right now all of that is going through the Onkyo receiver I have, and no matter how much "Works with Sonos" it says, it's far from what I'd call a "smooth" experience. I have no idea why SONOS isn't printing free money with their own switching gear, but having a receiver in the middle isn't optimal. What's the recommended way to connect all this and still have Sonos running all the audio? Pass through HDMI would solve this problem, but apparently that's a bridge too far...

What am I missing?