Pre=2000 Bonnevilles have a single muffler. The 2000+ Bonnevilles went to dual mufflers though. The single muffler is nice and really doesn't flow badly FWIW. Velocity through a muffler is hard to realize. For any sort of velocity measurement on a muffler, you probably benefit only at the top end.

If you're only battling drone at a low RPM, I think you're good to go with a resonator. Rasp with a V6 is common when you're revving, but otherwise V6 engines sound pretty normal. With some nice cam, your engine can sound awesome, though!