Hmmm, I have been playing my Katana with two 16 ohm cabs (8 ohm load) and it sounds pretty massive. Now that might make one think that it just sounds better with an 8 ohm load but, I also hooked it up to a single 16 ohm 4x12 and compared it to a single 8 ohm 4x12 and aside from just the difference in tone from type of speaker, I didn't notice any volume or fullness differences. I wonder if the splitter is causing a phase issue. Maybe try the 9 volt battery test thing.