The IR's (impulse responses) are used in the cab block. If you've added IR's to the unit, they will be in the user cab section. They are essentially, a snapshot in time of a specific cabinet, with specific speakers, with a specific mic and mic position. Use them with your FRFR. I probably would not use them with a physical speaker cabinet, as the IR is already doing that job of a mic'd speaker cabinet.
Also, if you're wanting to use a physical guitar speaker cabinet, you'll need a power amp (solid state or tube) to run it and no cab or IR block would be necessary.
However, you could run both... a cab block with IR to FOH and then a power amp and guitar cab on stage. Run each to separate outputs.