Be aware that Sonos speakers are not intended for PA applications. Any source you play has a 70msec delay, which provides a buffer to enable sync across multiple speakers. It can be very distracting to speak into a mic but hear your words slightly delayed. 
In addition, the human body is a great absorber of wifi signals. There was another thread not so long ago, also for a gym studio of some kind, where (as I recall) poor network performance resulted in them having to run Ethernet cables to the speakers.