I'm running my Shiva into a Germino 4x12 (16 ohm) and a Germino 2x12 (8 ohm). I'm running one 8 ohm output from the Shiva into the 2x12 (open back), and the other 8 ohm output into the 4x12. (I double-checked with Greg Germino and he said this set up is fine.) In this configuration, running both cabs at once, it seems to me that the 2x12 is producing a bit more volume than the 4x12. Does that make sense? Could be some kind of sonic illusion, but the 2x12 really seems a little bit louder to me. Both cabs are running the same Greenback reissues.