i’ve tried @Craig_Colthorp 's workaround and it worked but definitely sounded sub-par compared to addressing the HomePod stereopair directly via AirPlay 2. The workaround that works/sounds best IMHO is to
- use a Mac running macOS Monterey as the Roon Core
- in Control Center send all sound output to the HomePod pair via “AirPlay” (this actually uses AirPlay 2)
- turn off all OS sound effects and/or ensure they are not played through the HomePod pair
- instruct Roon to play through “System Output”
Compared to what Roon normally does for sound quality and fidelity, this is a travesty. But it does work and to me sounds best, under the circumstances.