Dolby Atmos - Possible with Dolby Atmos Soundbar and Original HomePods

I currently use my Apple TV 4K with a Bose 900 Soundbar. Over eARC, my Apple TV recognises the soundbar as Dolby Atmos capable and shows Auto (Dolby Atmos) in its audio output settings. When I try to simultaneously play Dolby Atmos/Dolby Digital 5.1 content to the soundbar over eARC and Sonos speakers via Airplay, the Apple TV outputs at LPCM 2.0 (stereo). This is because Sonos speakers are not Dolby Atmos capable (as I understand it). I am wondering if I pair two HomePods (stereo) with my Bose 900, whether the Apple TV would output Dolby Atmos to the soundbar and the two HomePods? I believe I have to select HomePods as the default speakers for my Apple TV 4K in order for the Apple TV to output Dolby Atmos content. But If I do this, I don't think I can play to the soundbar over eARC right? Right now the soundbar is the default set up (referenced as "receiver" or "TV Speakers" in the Apple TV default audio setting).

Before I spend close to 1K on HomePods (current price for these as they are no longer available retail), would like to get a sense if the above set up will work.

Thanks.