I’m not sure that your 3rd-party Receiver and the Sonos Ray will play in perfect sync for TV audio - you would have to test that in situ for yourself and see how that goes, but if you ‘group’ the Ray to a single Play-1 speaker, then ‘for sure’ there will be a minimum of ~75ms audio delay due to group buffering and so if the Play-1 is located in the TV viewing room, then you will ‘highly likely’ experience an echo-effect in that room. Of course the delay will not matter if you intend to use the Play-1 in a completely different room and away from the TV viewing room.
A way around the TV audio delay between the Ray and Play-1 is to forget ‘grouping’ altogether and instead look at the ‘bonding’ together of the Sonos speakers instead - BUT .. to do that, you will require two Play-1 speakers, rather than one, and bond them as left/right rear surrounds to the Ray.
Before going down that route however, I would first see if the Ray plays in sync with your 3rd-party Receiver.