Projector, 2 x Era 100, AppleTV Setup with IPTV

Very strange configuration issue that I imagine others have encountered before. We have an old Ben Q non-wifi, non-bluetooth projector hard connected to an AppleTV.  AppleTV connects remotely to two Sonos Era 100 speakers, configured in AppleTV settings. With Disney+, Amazon Prime, Netflix and Youtube, sound plays perfectly through the Era 100s and the experience is great. We also subscribe to an IPTV service and use the app (Smarters) they recommend which is available through Apple App Store. With Smarters, and other App Store apps for IPTV playing that we have tried, sound will play only through the projector’s speakers -- which is a terrible experience. I see no settings in any IPTV app to force/release audio through the projector speakers, and I see no setting on AppleTV that fixes this problem. So far this affects only IPTV apps -- we’ve experimented with a few now experienced the same issue with others, too.  Anyone else experience this? Is there an IPTV app (free or paid) for which this isn’t a problem?  Any workaround? Thanks.