You should be aware that in the type of scenario you're contemplating, you are limiting yourself to Dolby Digital and dts. Higher res audio formats like DD+, and lossless formats like TrueHD and dts-HD MA are all not possible (and I'll leave out immersive audio (eg. Dolby Atmos) as that will cause even more confusion.
Not sure what your source materials are, but if you're playing Blu-ray (1080p or 4K) movies ... you will not be able to get the high res audio formats (TrueHD, dts-HD) out this type of setup. Likewise, if you stream Netflix, you will not be able to get DD+.
There are two basic issues to consider. The first is that optical just does not have the bandwidth to support any surround sound format above Dolby Digital or dts. The other key problem is that, to enjoy 4K video (Netflix or Blu-ray or maybe you're cable provider). the entire chain has to be connected using HDMI 2.0 or better with HDCP 2.2. If any part of the signal chain is not HDCP 2.2 compliant, you will be forced to choose between 4K video and higher res audio.
In other words, you need to decide how important sound is to you in your listening environment (and I mean this non-judgmentally). I did read your earlier comment, but I am not talking about super high-end here. If you hear a difference between Spotify at normal quality and Tidal, or between Spotify at normal quality and a CD ... that's kind of what I'm suggesting the order of magnitude is here. There are better experts on here than me who might do a better job of explaining it. If it's not that important, than macgyvering something together using your soundbar as a component is probably fine. But, if you place value on audio quality then you really should look at not just a receiver but good speakers as well as timbre matching across the entire front soundstage is pretty important (in other words, mismatching the centre from the L/R is not recommended).
If you are intent on including the soundbar as the centre speaker, then you need a receiver that has "pre-outs" and something like
this to take your centre channel line out and provide an optical in to your soundbar. However, one really quick way to drive up your budget is to limit your receiver choice to those with pre-outs. That's a feature that is generally found on substantially more expensive receivers that are likely overkill for what your sound quality expectations are.
Lastly, while not a fan of wireless surround sound, I am forced in my current environment (at least until I replace the flooring) to do the same. I have tried several units (including the Rocketfish one linked above) and found most of them deficient in some striking ways. The only one I have been somewhat satisfied with is the Soundcast unit (
https://www.amazon.ca/Soundcast-SCS1.../dp/B003F7R7SI).