It's more general than FRP so is better at stuff like simple async coordination (what most people use promises for). But you can easy do FRP-style stuff on top of channels, which is basically what transducers are. So they are closely related, but have different roots.
Rather than saying that CSP is more general, I'd say CSP is more provides you a more low level constructs. In FRP signals are the key concept that represent value that changes over time. Signals have a pushed based interface that's kind of why it's reactive. FRP typically provides pure functional interface, meaning you never put values or emit events, you just have control flow structures that allow you define transformations over base signals. FRP signals can be easily implemented via CSP channels, but not other way round, that's because CSP channels are push based for the producer side and pull based from the consumer side.
If I had to make an analogy channels would be queues while signals would be an observable variable.
