It really depends on what you expect out of the sound. If you want a quiet sound, put a single tailpipe with a stock muffler. If you want a raspy hotrod sound, use duals with straight pipes. All sounds out the back depend on a number of inter-related items.
Cubic displacement, modifications to head, carbruators, size of headers , diameter of exhaust pipes, etc. You see any combination of these will alter the sound of your inline. Find a guy or gal with an inliner that sounds good to you and go with that. Participate in shows and clubs and you will find your way.
I like to hear a motor at it's best level. Nice low rumble at idle and able to talk to your passenger at highway speeds.
