You’ve got a couple of things going on.
First, why can’t you still use your PLAY:1s as surrounds, and just place the Era 100s elsewhere? I don’t think I understand your comment there.
Second, what kind (codec) of signal is your new projector putting out, and how? The PLAYBASE is restricted to Dolby Digital (due to the optical connection) and can’t receive Dolby Digital Plus, or Atmos, both of which require ARC or eARC.
Essentially, due to the restriction of the optical connection (and likely the CPU in the PLAYBASE, but that is really secondary), the best the device can process is Dolby Digital, or stereo, even with streaming music.
I think that is likely what you’re running in to, but if not, let us know.