How to connect a soundbar to Roon? Via a Raspberry PI? Will Roon use all 5 speakers or only 2?

I have a Samsung not-so-smart TV connected to an Nvidia Shield.

I am thinking of getting a soundbar like the Sony HT-ZF9 (I don’t want to get a dedicated system with amplifier etc) and I have a couple of questions:

  1. Both the Shield and the Sony Soundbar have chromecast. Therefore I can play Roon music via either; the difference should be that, if I output from Roon to the Shield, the TV screen will turn on and display lyrics etc; if I output from Roon to the soundbar, the TV shouldn’t turn on. Is this right? The difference is not trivial because it means I can play background music without kids being attracted to the screen!
  2. In another room on the same floor I will have two speakers connected to a Raspberry PI / HifiBerry running Ropiee. Is it correct that Roon cannot play the same music to both a Chromecast device (be it the soundbar or the Shield) and the HifiBerry?
  3. If (2) is correct, what is the best way to get Roon to output to the HifiBerry and the Soundbar at the same time? The soundbar has an optical audio input and an analogue 3.5mm jack input. I guess I can set up a Raspberry Pi with the HifiBerry modules and connect that to the soundbar? Something like the HifiBerry Digi + or the Hifi Berry Dac ? Would digital be better than 3.5mm jack or would there be, realistically, little difference?
  4. Will Roon play music only on two front speakers or all on 5 speakers? Roon has this explanation but I admit I didn’t fully understand it. In my case I would be playing two-channel music, and I want to understand if the left channel will also be played on the rear left speaker, too, etc, or if only the front two speakers will be used.


PS I know B&W has speakers and a soundbar which should support Roon natively, but they are too expensive.
Also, the HifiBerry digi+ was recommended in a similar question on another soundbar, so I imagine it could apply here, too, but I’m not too sure