[Dean]

Here is a thought. Take off the axle back and see what it sounds like. It will likely be louder than you want, but will give you a feel for what the tone and burliness of louder is. If it is acceptable but needs to be muffled, a straight through can of some shape muffler and some fab work will deliver for cheap.

You could also drop the mid pipe for kicks.

If you don't like the sound, you have to look for UEL options.