From the description you give, it doesn't sound as if it needs to talk to the Zephyr. Your brake section must have both rails gapped on either side (4 total gaps). One side of the DPDT goes to the Zephyr track outputs, the otehr side to the output of the Roco brake unit, and the middle to the rails in this insulated brake zone.
Not all decoders respond correctly, I assum since the Roco unit slows the train rather than just stops it, it is sending DCC commands on address 00 which is supposed to be a broadcast address. Decoders are supposed to respond to this but not all do,
I haven't read the isntructions on this yet, this is just based on what you said about the trak being hooked up to a DPDT switch.
--Randy
Modeling the Reading Railroad in the 1950's
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