I have read that 4 speakers, each at 4 Ohms, put in parallel in Sonos Amp is flat out not possible. Even 6 ohms each would not be possible. The requirement is 8 ohms, so the total net load is at a minimum 4 Ohms. But all of the discussions are for parallel speaker configurations.
What about 2 speakers, 4 ohms each, connected in series on each channel? I am not an audiophile, and not sure what that would do to (a) the sonos amp and (b) general listening quality.