Yeah....I do need a muffler. I still love the sound, and it's quiet for me unless I open my window, but there is a definite rumble for the people sitting directly behind me. So, sound-proofing the firewall and doghouse, and a muffler, are solidly on the list
The stack, on the other hand, is what makes my bus "my bus". My wife even agrees. She just wants it quieter.