All Sonos subwoofer versions are compatible with the Arc.  Note that you will need at least one Sub Gen 3 to have 2 Subs in one Home Theater room. 

If I have a Klipsch sub woofer, how would I connect it to my Sonos system? 

If your Sonos system includes a Sonos Amp that is not being used to drive surround speakers, you would wire the Klipsch to that. Otherwise, you wouldn’t be able to use it. 

Thank you. So I would have to purchase a Sonos amp to be able to do this then,?7

A Sonos Amp has a subwoofer line level output that can be connected to a powered Sub. It does not power the Sub itself. I have no idea which Klipsch Sub you have, so it’s hard for me to look up any specs and be more concrete. Unfortunately, I’ve never looked in to the Klipsch line of speakers. 

In a set up with an Amp as fronts, Sonos does not cater for also using a soundbar.

There is no way to use the Klipsch subwoofer with a Sonos Arc. 

Thanks for the information.. so I guess I have to purchase a Sonos amp the and I will see what happens.