If this projector doesn’t have an ARC or eARC output, or even an optical output, your best bet is to separate the audio before it reaches the projector. A standard HDMI switch with an optical output could be used to carry a Dolby Digital 5.1 signal to the Sonos adapter that connects to the Beam. If you’re interested in getting Atmos input to the Beam, there is the HD Fury Arcana, the Feintech VAX04101k, and the latest, is the OREI HDA-935. You can also order from those links from the companies directly, or check your local retailers for availability. Amazon may carry some, depending on location.

If you’re to look in the Home Theater section of this forum, you’ll find a lot of similar threads to this.