I suppose that using an empty FX rack would free processing power.
It is possible to use external VST plugin by routing the signal into Stereo input for exemple.
In this exemple I use a VST time based FX plugin (delay), routed to input 11/12 of my CQ12T set to digital input.
I then route a mic (or more) to this VST plugin.
The ST1 fader in the CQ become your FX fader.