Hi @kgagliano
Port is not designed for TV audio - because it expects an audio-only source, it makes no attempt to stay in sync with your TV picture. In addition, Sonos products are not designed to work in concert with third-party Home Theatre setups.
The best way to achieve what you describe is to connect one of your Amps with an HDMI cable to your TV’s HDMI-ARC port. That Amp will be in sync with your TV, and the feed can be played to other Sonos rooms, but please note that synchronisation will be lost as the feed is shared over the network - this is not something that can be done immediately, and without buffering. If you are unable to hear the Amp that’s connected to the TV in the other rooms, the audio delay will not be an issue. If you can hear that Amp and another at the same time, it will likely sound like an echo. You would not be able to include your third-party receiver in this setup.
Another option would be to replace the Port and third-party receiver with a new Amp or a Sonos soundbar like Arc, as suggested by the BestBuy employee, who, for the record, was not wrong.
I hope this helps.