Sonos controllers and players need to be on the same IP subnet. If the annex router is still acting as a router it will split your network. To start with, switch it into access point mode. Modern routers typically offer this as an option. If not, search “router as access point”.

You didn’t say how your house Sonos is operating: whether in (a) wired/SonosNet mode or (b) wireless/WiFi mode.

If it’s (a) then wire at least one Sonos device in the annex.

If it’s (b) then configure the annex access point (router) SSID to the same name/password as in the house.

Ratty. 
         Thanks for the reply. I’m not to sure I completely understand what I have to do but basically you are saying the the annex is just an extension of the house WiFi not a new network.  The house is an all WiFi System.  I’ll have a go with it and see how I get on.  
thanks again. 

Yes. You don’t want your annex to be another ‘network’ (in the strictest sense); you want it to be another wireless ‘segment’ on the house network. Hence the direction to switch the annex router into an access point, thereby disabling its ‘router’ functions. 

What make/model is the annex router? 

Hi. My annex router is a. Tp-link Archer c6

https://static.tp-link.com/2020/202005/20200514/1910012695_Archer%20A6C62.0_UG.pdf

Section 4.4 on page 21

Ratty

         Thank you for your help.  Ultimately I was trying to set up my Sonos system in the annex as well as keeping Sonos in the house.  It seems laptops iPads phones etc made the connection easily but the Sonos proved somewhat more difficult but now thanks to your help it’s all up and running. Thank you again your a star.  
 

dusty 

Hi Sonos i really need help with my SYMFONISK table lamp speaker, I've been having so much trouble wirelessly connecting it to the wifi without the need to use the Ethernet cable, I thought I had figured it out but it seems to only make another problem for me.

In Sonos app system -> network -> wireless setup

I connected my wifi wirelessly successfully? And it told me to disconnect the Ethernet cable afterwards but when I do it says its not connected to the wifi.

Please help me with this i love listening to it, it sounds amazing with the bass up high

Need to get my sonos system robust. I plays for a while and then it stops.

It seems that if something starts (like a Microwave, etc...), it sends a quit signal and then my laptop application tells me that there is no more Sonos to find. 

That “quiet signal” is wifi interference. Try changing your wireless channel or/and move Sonos and/or laptop away from microwave.

https://support.sonos.com/s/article/3286?language=en_US