You’re probably going to need a better understanding of how the existing system in the house works. It doesn’t seem likely that there would be a direct connection between a 3.5mm socket and a Cat5 network (one is typically 3-wire, designed for line-level audio, the other is 8-wire, designed for high-speed digital data), so there are almost certainly other devices present that you can’t see.

Once you know exactly what equipment is present (i.e. make and model numbers) and how it’s interconnected, you can then start to make decisions about how to connect up to it.

If you have all of the components shown in the diagram, that is a complete multi-room hardwired system already in place. It’s not obvious to me what you would gain by adding Sonos components to it.

The main problem you could expect is that if you add Sonos speakers in addition to hardwired speakers that are (presumably) already there, you will get a noticeable time delay between the two (Sonos add this so that they can compensate for variable delays in a wireless network).

If you want to add a streamed (over the Internet) source then that would need to be plugged in (at Line Level, not amplified speaker level) at one of the RIM modules.

Sorry I’m new to all this. 

I do have all the components in the diagram. I have used the sonos amp in another place and really liked the system as it was easy to add extra speakers and control media from my phone. 

But maybe I need to look at something different?

Thanks again for your help. 

Depending on how well you get the existing system working and how well you like it you might abandon all but the speakers and replace the rest with Sonos devices.

If you keep the present gear you could easily feed it from a Sonos Port and have the best of both.

Speakers are high power devices, the 3.5 jacks are designed for headphone power levels or less so going between the two without a converter device isn’t likely to work.