help a traktor guy new to RB FX [DDJ-FLX4]

Is there a way to manipulate volume of a post fader fx with the trim knobs? i was able to do that with previous controller and before that with a dj mixer. Maybe im missing a setting?

Sorry to bother i come from a NI controller which was my 1st but sadly only lasted for a year before starting to break (S2 MK3, dont buy that even if you casually use fx).

I have lots of questions being new to pionner/RB so please bare with me.

I'm having a hard time deciding if using standard fx unit, Smart CFX or performance pads for transitioning between songs with echo (what is RB equivalent for double delay?)

Thanks,
Nicolás