Tightrope components
I figured this out while setting up a new channel on an existing system. Tightrope confirmed it for me.
FrontDoor -> Cablecast Server -> Cablecast Channel -> Servers (e.g. SX Player)
FrontDoor -> Carousel (resident on Cablecast server if shared with a station, or on Carousel server if signage only) -> Carousel Channel -> Carousel Player -> Carousel Display Engine