I tried the Seymour Duncan MM pickup mod in a 4-string...took the balls right out of it! Worst idea I 've had in a long time. I've thought about adding a J neck pickup to my MM too. Try adding that first, then worry about the MM pickup. Don't know how the stock MM preamp will react to the additional pickup though. You might think about switching the preamp (Aguilar OBP-3) if you can't get the stock one to work.