I would try to connect both the Assist and the RSA2 to the CB200, both on ex-bus protocol,using receiver 1 and receiver 2 connections. Important to set CB200 to be ex-bus input and the Assist and RSA2 as ex-bus output.
I don't like that use of double chaining the receivers, and I like even less the fact that you are using both ex-bus and ppm as protocols to talk to the CB200.
One mention about failsafe. I'm not sure where you are programming failsafe, but my practice is to set it on the CB200 and turn it off all together on the receivers.
Field ready: Taborca (3.4m), ASH-26 (5.4m), Piper Cub (2.7m), Ocelot (1.6m), Alula (0.5m)
Factory line: Carbon Cub (2.2m), A6M Zero (1.6m), Fieseler Storch (3.3m)
Design phase: Szd-20x Wampir II (7.5m), Rutan Quickie (1.6m)
Dreaming: Weird push-pull called Double Trouble (2.7m)