HomePod Mini, Apple TV 3rd Gen and Airplay cause HomePod to cut in/out

Has ANYONE ever been successful using both an Apple TV 3rd gen in unison with a HomePod Mini as airplay speakers?

I like to control my music using the Remote App and send it from a Mac mini to a 3rd gen ATV and that works fine. Or I can send it to the HomePod and it is good. BUT, I f I send it to BOTH speakers, the HomePod cuts in and out for minutes at a time.

ALL software/iOS and OS is up to date including the router.

After 30-40 minutes on tech support with Apple, turning off everything else in the house that was an apple product, still no luck. [ when it came time to restart the phone I was talking to them on - they never called back. I found out later that evening they tried calling my wife's phone 4 times ¯¯\\_(ツ)_/¯ ]