There will be a 70msec delay on tv sound to the Era stereo pair, causing a kind of echo. Additionally, they’ll play stereo, muddling any 3-channel sound from your Beam.
 

Instead, set up the Eras as a stereo pair and use just them for music, and the existing setup for home theatre.
 

You can also try bonding the Eras as the surrounds instead of the Symfonixs and see which you prefer.  

You cannot improve sound by grouping “front” speakers and using the soundbar as a center.  A soundbar already has the L/C/R speakers, so the soundstage will be dispersed and muddy.  Also, the “front” speakers will lag behind the rest for TV sources.  Just don’t do it. 

Agate,

Have you actually heard a Stereo “grouping” with the Beam2 and saw no improvement in dispersion to a wider front “sound stage,”  Why would you not get Atmos from the Beam sound bar and Era 300s surrounds, but an improved front sound stage with the addition of front stereo pairs. Maybe by adding the front stereo pair the sound would be closer to the Arc, than not having the them at all.  I’m just trying to use my Symfonixs rather than  spending $800 for an Arc, disposing of them, or using them as satellites in other rooms.

You wouldn’t get an improvement because you would have two discrete channels coming from 4 discrete point sources.  That’s not a “wider” front sound stage, that is a muddied front sound stage coming at you from 4 directions, doubling up on the R/L and overpowering the center channel. It’s also going to be echoing for TV sources.  Use your speakers in another room, or sell them on e-Bay.