Thanks for the clarification.
When you had the Time Capsule setup to operate in Bridge Mode, the Technicolor modem/router was providing DHCP and NAT services for the entire network.
So, when you set up the Sonos system, the Sonos device was configured to receive DHCP and NAT settings from the Technicolor modem/router.
In Bridge Mode, the Time Capsule simply passes through the settings that it receives from the Technicolor modem/router to the Sonos controller.
When you changed the setup of the TIme Capsule to also provide DHCP and NAT services, the Sonos system could then no longer receive DHCP and NAT settings from the Technicolor modem/router.
So, you have a couple of options:
1) The simplest option is to change the Time Capsule back to its original Bridge Mode settings, so the Sonos system will then pick up DHCP and NAT information from the Technicolor modem/router.
The downside....you lose the Guest Network option on the Time Capsule. Maybe you could use the Technicolor modem/router to supply the guest network function?
2) If the Guest Network option on the Time Capsule is important to you, then you will have to start all over again from scratch on the Sonos System and configure it to work with the Time Capsule to pick up DHCP and NAT from the Time Capsule.
I don't have a Sonos system, so I cannot tell you that the Sonos would work correctly in this type of arrangement. Technically, it should, but as networks go, you really won't know if this will work correctly or not until you try.
The downside.....you are trying to run two routers on the network in this type of setup, with both trying to provide DHCP and NAT services.
Normally, you only want one device on a network providing DHCP and NAT services, because the network runs more efficienty this way, with much less chance of network conflicts and errors.