The RackUltraFX rack supports dual mono, but only some of the units you can load into the rack support Dual Mono.
As far as I’m aware the units that support Dual Mono use are Saturator and Amp+Cab Distortion. This should be in the Firmware Reference Guide Ultra FX appendix but it appears that it isn’t. We’ll look into getting that updated.
And careful with Saturator in dual mono if inserting it into 2 mono grps. In some cases it might bring the desk down. I was told the case is being investigated.
I’ve also tried using the Amp Simulator in “dual mono” mode and gotten very weird and undesirable results. I’m not sure “dual mono” is ready for prime time yet with UFX slots.
I’ve submitted a support ticket with A&H about my situation…..