You cannot add any more front speakers to a Beam setup. The Beam alone already includes the center, front left, and front right channels. You could group more speakers with the Beam, but you will likely experience a slight audio delay from the grouped speakers when playing TV audio. Although streaming music will be in sync.

The Beam should have good balance for the TV viewing.

For music you could easily add more Sonos speakers to the room, in matched pairs so you can use them as Stereo Pairs.

The 100s would work, Fives would be a lot better. With the 100s I’d really consider at least a Sub Mini to get good music reproduction.

With this setup you could Group in the Beam, it would be in the center but still producing the left and right channels.

Also, if you grouped them with the Beam, they would have the audio at minimum a 75 Ms delay, for the TV  input. For streaming music, they’d be in sync. That’s the audio delay @GuitarSuperstar was speaking about. 

Thank you all three of you for responding.  It all makes sense so I won’t be buying the extra 2 Era 100’s.  It’s a shame though, as the Beam doesn’t do a brilliant job of channel separation either side of the TV.

That’s why I went with an Arc, not to mention the upward firing speakers used in Atmos. I prefer the wider soundstage on my larger TV. 

It is easy to fit the Beam into another room, even one without a TV as it makes an excellent small speaker.

That leaves you a nice spot for an Arc picked up at a pre-Christmas sale.

What the heck…spend the $799 (maybe $764 at 15%) for an Arc on sale. I’m sure the OP has it laying around somewhere. 

I just couldn’t resist poking the bear on that one.

Happy Holidays!!!