The Sonos Amp has an analog input, but no line level outputs, only the powered speaker terminals. You might connect a line out from the Onkyo to those analog inputs, but there’s no great way to get a Sonos signal from an  Amp into the Onkyo, without a Port. 

What were you thinking of doing by connecting them to your Onkyo? What inputs and outputs are available on that Onkyo?

I was trying to connect everything on to one system and be able to control music through Sonos app. I actually bought the Denon AVR -S760H instead on the Onkyo. Can I still do it? I would like to listen to music when not watching tv through the 5.1, can I just use my Sonos Amp to connect to the 5.1surround sound and not the Denon receiver?

As @Airgetlam explained this is not possible. You could connect a Sonos Port to the Denon though.

Hi. It seems to me that the whole idea of connecting an Amp (which has an amplifier)  to a receiver (which also has an amplifier) has to be misguided.

As others have said, a Port is more likely to be suitable.

Does the AVR have a Tape Out / Rec socket?