Can you explaining what you mean by ‘Bridge mode’? 

The Sonos Amp has a line level output for a sub, so the sub needs to be self powered. You shouldn’t connect a sub to the powered output of the Sonos Amp. 

And yes, i can connect a passive sub or not?

I would not recommend connecting a passive subwoofer, no. 

I would not recommend connecting the two Amp channels together.

That is a feature some amplifiers offer but it is usually spelled out in the owner’s manual.

You could call Sonos support to verify it would or wouldn’t work.

Thank you Stanley that is exactly what I need to know. I appreciate it.