I'm afraid there are a couple of ways in which that won't work wxactly as you want, but there are still good options.
You cannot use a Beam as a centre speaker. The Beam does front L, R and C. Or you can use an Amp with L and R speakers and a 'phantom' centre.
If you use the Amp and speakers for the surrounds then you cannot use a third party sub. You could use a Sonos Sub.
If you use the Amp for front L and R you can use your sub. Then use a pair of Sonos powered speakers for the surrounds. Or a second Amp and speakers.
The Playbar has no HDMI connection, only optical
Thank you for the answer,
Then I think the best option would be using the AMP as L and R and then using a Phantom center.
Do you have any idea of the quality in this setup, will the amp phantom center be as good or close to a real allocated center speaker?
Again thank you for the very detailed answer.
Hi. I don't have any personal experience of the Amp so i shall have to defer to others. But I understand it's accomplished by splitting the centre channel to L and R, which I would have expected to work well.