I have a ARC, Sub, two One SL, and just picked up 2 Era 100s. I didn't realize that you can't add more than 2 surrounds when I purchased the Era 100s. The idea was the create 7.1 surround here which I guess is only truly achievable buy purchasing the Era 300s. But the price tag on those is insane for two of them. As a work around I have the SL ones now configured as stereo only and the Era 100s are now my surrounds. I can get the stereo only pair to play along with the setup but it's super annoying to have to use this work around. When will we get an update to enable 4 surround speakers without having to do this work around? If I had known about this earlier I wouldn't have purchased the additional units. They also can't be controlled with the same remote unless you purchase a third party remote to control them at the same time or manage the sound directly through the app. So everything I turn the TV on I have to manually group the additional stereo only speakers to the rest of the system. 

Please update this sonos. I've seen many posts about this and I can't imagine it's not possible with firmware and software updates.