If you use an optical audio splitter / extractor, you can go optical to the Beam via the Sonos Optical to HDMI adapter that should come with the Beam. This will get you 5.1 sound.

Something like: https://smile.amazon.com/gp/product/B093H3GFR3

To get Atmos is going to be more expensive, probably around the price of the Fintech, possibly a little lower, but not in the 50-70EUR range yet.