a) Cascade via the 2-wire interface with an XRL cable (only supporting some brands such as Clear-Com and RTS)
b) Cascade via the 4-wire interface and a 2/4W converter: Connect to the Solicom C1 Pro via the 4-wire interface and to the wired intercom system via the 2-wire interface.
The 4-wire interface of the Solidcom C1 Pro is line standard. You can always cascade the Solidcom C1 Pro with another wireless intercom system via the 4-wire interface.
Please check whether there are 4-wire options in the group. If not, you may not hear the sound from either of the devices. Please also check whether the 4W definitions of the devices are correct.