I've heard a few people comment that their boomtubes aren't much quieter than straight pipes. I've ridden by 796 with no mufflers (straight shot out of the midpipe) and the sound was unbearable. Exceedingly loud and obnoxious - wore earplugs and didn't dare go over 4K RPM in fear of ear damage. Did you ever hear your 696 with no mufflers? How does it compare to the boomtubes?
My M620 with no mufflers was really really loud . . . activated a few car alarms up to blocks away . . .