I installed an Agostini muffler on my Norge. With the DB killer in place, the sound was muted but better than stock. With the DB killer removed, the sound was glorious! Not too loud, but loud enough so you could hear it over the wind and tire noise of cars around you. Think manly and authoritative.
My Norge ran well with or without the DB killer (certainly as well as with the stock muffler).
Check YouTube for some videos with sound.