Any Sonos speaker used as a Surround does not produce  dialogue. Any Sonos speaker not associated with a Sonos home theater will have a 75ms delay to receive the dialogue from a movie source. However when playing music there is no delay to a speaker not associated with a home theater when grouped.

While playing a movie or TV show with surround, the dialog location is at the director’s discretion. Dialog is rarely sent to the rear, but I can imagine an occasional scene when an actor enters from the rear.

If you are looking for an option to send all or part of the front dialog to the rear speakers, the surround configuration does not support this.

“When watching a cable tv show with a beam” how is an era 100 involved? 

@rugrunner 

Has your question been answered by at least one of the responses?

I recently had a beam and 2 era100 speakers installed by a professional.  The sales person knew I was buying the additional speakers to have better dialog sound.  But when installed they had no dialog.  I was able to return the speakers.   Now I would ask.    is there a sonos additional speaker that does duplicate the beam sounds (including the dialog) that the sales person was not aware of?    

No. 
the Beam provides the 3 front channels and that’s it. Nor does Sonos enable individual volume controls for those channels. 

I wouldn’t consult with that sales person again