TRS 1/4 balanced cables will not work, because the Fb uses Unbalanced jack I/O's
Use Unbalanced jack's to connect the FB.
It might 'look like' Out1 can feed a 1/4 TRS balanced jack, but that is because Out1 is desiged to 'remove*' Filter1
from main out when a mono(!) jack is plugged there. (*Parallel modus) So on the jack ring contact the 'pre-VCA filter1 signal' is present, but it is not intended to get out of the box, it is intended to be shorted internally to ground with a Mono jack is plugged in Out1
Off coase there can be creative applications to use that signal externally anyway, especially in modular setup.
Inserting the FB directly after any synth works very well.
If the desk is an audio I/O interface as well, it must be possible to send audio from Cubase to the FB and re-record it.