BenQ projector + blueray + playbar=TRUE?

Well, yes and no. Where are you connecting the optical connector from the PLAYBAR to, the BenQ projector, or the Bluray player?

In either case, the bluray player needs to be set to Dolby Digital, as the PLAYBAR won't work with DTS. Unless your bluray player does transcoding, and there's a thread about that, you may have difficulty with some portion of blurays that don't have a Dolby Digital soundtrack. And if you're connecting the optical connector to the BenQ, I'd assume there would be some audio settings on it, so you'd need to set the BenQ to also be Dolby Digital pass through.

Hi.

The BenQ dont have optical so my plan was to have HDMI from BenQ into Blu-ray player, and connect sonos PLAYBAR with optical into Blu-ray player. In my head this will connect all 3 components. In addition i got a Chromecast into the 2nd HDMI port in the blu-ray player that i use for netflix and casting other stuff. Does this sound like a working solution?

Sure, as long as everything is locked down to Dolby Digital. I've never heard of a bluray player that has extra inputs, but that's pretty neat. Of course, there's nothing quite as certain as testing, especially in your case before you mount anything in places that it's hard to get to. At the end of the day, if the secondary input doesn't work, you could always get one of the "splitter" devices that people use to take the input from everything and pull out the optical, before it sends everything via HDMI to the BenQ.