Your salesperson at BestBuy was misinformed, the Era 300 series will not connect to the Sonos BOOST.  Especially in surround mode, which is completely separate. It’s much more likely you have some wifi interference or possibly a duplicate IP address issue.

While in surround mode, the surrounds (any of them, including the Era 300) connect to the Arc on a hidden 5Ghz channel. A BOOST would not impact that at all. I’d take a look at the linked FAQ before spending any money, and at the least, perform a network refresh by powering down all Sonos devices, then rebooting your router. Once the router has had a couple of minutes to reboot, plug back in your Sonos devices, starting with the Arc. 

thank you for the reply i will give that a try tonight.   Will Plugging one speaker directly into my router do anythign?

It creates a ‘SonosNet’ environment, but the Era speakers are unable to ‘see’ or ‘join’ that, they’re designed to connect to the normal Wi-Fi signal from your router, or when in use as surrounds, a hidden 5Ghz channel from your Arc. It’s essentially the same thing that the BestBuy employee was erroneously trying to force by the use of the BOOST. 

Just as an FYI...you cannot Pair Era 300’s to your Arc. The process during setup of a Home theater wherein you have the Arc and sub with the Era 300’s as surrounds is called Bonding. 

Paring is the term used when you combine two Sonos speakers of the same kind as a Stereo pair. For example:

• Two Five’s
• Two Era 300’s 
• Two Era 100’s
• Two Sonos One’s 
• Two Play 1’s
• Two Play 3’s 

So are your Era 300’s used as surrounds or as a stereo pair?

Hi @Alleddie 

Welcome to the Sonos Community!

I can see your Era 300s are in a stereo pair as @AjTrek1 maybe suspected, which means that unlike with other input sources which will group successfully thanks to buffering, TV audio does not group with other speakers well as your Arc is unwilling to wait for buffering, as that would result in a lip-sync issue with the TV. It does work, but performance is entirely down to local conditions which may or may not be possible to improve. So, although not everyone has issues in this situation, it is somewhat expected.

As @Airgetlam rightly pointed out, a Boost would not help in this situation, as the Eras will not utilise SonosNet. On WiFi, Arc will be connecting to the slower 2.4GHz band on your router, so assuming there is no interference anywhere, the only thing you can do to possibly improve performance is to connect the Arc to the router with an ethernet cable.

Please note, however, that interference could easily be a factor. If music sources play in sync across both rooms without issue, then you can worry less about it. Interference at the Arc, the router or the Eras would cause issues, and our Reducing wireless interference help page can help you identify sources.

I hope this helps.