Thanks allot JTUK
So if I understand correctly, I should use the right speaker out jack with the switched put on "dual mono" .. That is what I originally thought but when I switch of my amp having it connected in above mentioned way the cab makes a strange like fizzle sound and doesn't do it when jack is connected to left out on amp..
Looking here http://support.swramps.com/manuals/pdfs/procabs_om.PDF it seems my impedance on cab is 4 ohms