A:Answer You can have a total of 36 zones within the SONOS environment. A zone is defined by a SONOS speaker pair, a PORT, or an ARC/BEAM 5.1 or 5.2 (BAR, Surround Pair, & SUB).
As for the PORT and receiver combination, you can connect as many non-SONOS speakers to your receiver as you wish, so long as they are adequately amplified. The PORT connected to the receiver allows you to integrate the receiver into the SONOS system.
To further explain that integration, let's say you have speakers in your home, on your back patio, and near your pool (Port with receiver and non-SONOS speakers connected to the receiver). Within the SONOS S2 app, you can play the same music on those three zones simultaneously. The above explanation is just one example setup.
As for your original question, it'd be pointless to connect SONOS speakers to a receiver if you're wanting to achieve optimum sound. They should either be setup as a speaker pair (Assuming One or One SL, or FIVE), or be connected to a SONOS AMP (Architectural series).