Hi @Willy
I don’t know how to explain it any more simply, but maybe it will help to go into more detail (?!)
Every RackFX unit can be used as either an insert (inserted directly/inline into an input or mix channel at the insert point) or used as a Mix -> Return (where the FX input is fed from an Input Direct Output or a Mix Output and the return is one of the 8 stereo FX returns).
You set this using the ‘Back Panel’ of each FX unit.
All of this is discussed here – https://www.allen-heath.com/media/SQ_ReferenceGuide_V1_5_0.pdf#page=53&zoom=auto,-361,573
In this instance, to use two FX unit’s on a single group I’ve suggest using both methods at the same time, so one FX unit is being used in the group channel and one is being fed by the whole group output.
The signal path is therefore:
Input channel/s > Group > Insert point output > FX unit #1 > Insert point return > Group output > FX unit #2 > FX return
Cheers!
Keith.