I tried a couple single in dual out mufflers on mine and it droned like a dog. I swapped the original bus muffler back on until I can go true duals. I personally think the 2 into 1 stock set up is problematic for drone when adding an aftermarket muffler. (personally, my opinion). The single 3 inch pipe is a joke. What's that 1.5" per side?
I am not convinced that the downstream resonators make that much of a difference. I mean sure, they do. But do they? I think the source of the drone is that single 3' pipe. That's why that bus muffler is needed to quiet it down.
Not the answer you were looking for. Just wanted to comment.