Hey @John010.
I too have a Denon HEOS Amp and also a clutch of other HEOS speakers, some wired, some WiFi. I too was interested in integrating them into Smartthings but I only got as far as using the DLNA Player project to get them connected. I then used BigTalker2 to trigger a HEOS message if a movement sensor was triggered. Then I stopped, a lot of work and troubleshooting for little benefit I felt and we mainly just use the HEOS speakers from the Spotify app so the kids can play different music in different rooms.
I’d be interested in learning and doing more though, so please come back and share your own experiences.