My surround system is comprised of the Arc SL, a sub and two ERA 300s.  The 300s have microphones.  But the microphones are disabled by default since they are rear speakers. I have no other way in my lower level of using microphones for Alexa or the Sonos Voice control.  Is there a way to enable one of the ERA 300s to use its microphone as a smart speaker?  I would hate to have to buy an ERA 100 just to have a microphone capability and the lower level of my house. Any help is greatly appreciated.