the mufflers that come in the kits are trash, may as well throw those in the scrap bin. I'd spend the money on either a FTE resonator or a MBRP "quiet tone" muffler. I have both a 12" FTE resonator and then the quiet tone muffler and I'm thrilled with the result after being straight piped for 5+ years. you tell yourself it doesn't drone in the cab, but holy hell the difference you notice when it's not there anymore. my LBZ still has a nice low idle and it's definitely not much quieter than the straight pipe was at idle, but off idle and under acceleration it is somewhere between stock and straight piped, with zero drone in the cab.
if you want more volume, run just a resonator, won't cut the sound down by much but the lack of drone is worth every nickel