It won’t help, I don’t think. 

In a home theatre system, there are 3 front channels: Left front, Centre and Right front. The centre channel is typically the dialogue channel, other than when the sound mixer has moved dialogue to match the video signal - eg an actor at screen left may have the audio directed more to the  left front speaker. 
if you add them as surrounds, you will only hear “effects” from them. There’s no way to select the dialogue channel and send it to the surround speakers. 
Adding those speakers as another room and grouping them is likely to end with muddled sound. The way Sonos achieves synchronised multi-room sound is to buffer a bit of audio data before the speakers start to play. This delay is minimised in a home theatre system to avoid lip sync issues, but will be present with rooms grouped to a tv signal resulting in a kind of echo effect (though not an issue for streamed music). 
Have you tried toggling the Voice Enhancement feature and/or the Night Audio one, to see if that helps you?

Thank you for the quick reply and information. 

No, I had not tried your suggestions but I will now.  My thinking was having additional speakers closer or behind my typical viewing location might help which is about 12ft from my sound bar.

I had also found a deal on a pair of 100's which caused me to give this idea a little more thought.

Thanks again

Sonos devices can become addictive. If it’s a really good deal, get those 100’s and use them as surrounds, or as a stereo pair for music listening. You’ll soon have them all over your property! 

Several folks have requested the ability to boost the center/voice channel on the Arc/Beam to deal with poorly mastered sources that are hard for us geezers to hear.

A method that does help a bit (on top of the settings mentioned above) but lacks spousal approval is to cover the side channel speakers with several layers of towels. Might have been wiser of me not to use my bright yellow microfiber ones.

Ok, thanks. I'll take that into consideration :-)