You may want to check the amp/receiver you’re using as it may have a mono mode.  Not trying to say that mono mode on the Port is a bad idea, but it would be a better feature on an amp since it would impact all input sources, not just the Port input.

Unfortunately my amp does not have it, hence the request. 

It used to be a common feature in stereo amps, I don't know why the change these days. Cost reasons I guess.

Hi @garyhooper, welcome to the Sonos Community!

I’ll be happy to pass your request for a dual-mono mode on the Port to our development team :)

With the S2 update today, the Port now supports Dual Mono output: https://support.sonos.com/s/article/3521?language=en_US

Now that is what I call a fast response to customer feedback!