I can't believe those Macs are still on the selling block. Love mine!
OP, if the loudness is the issue, why not go back to the catted H-pipe? I'm running mine with a Bullitt H-pipe (same as an OEM one w/a smallish obstruction in the middle). The exhaust note at idle is perfect. I feather the the gas coming/leaving my neighborhood. I don't want to be that asshole with the loud ass Mustang either. At WOT they sound beast.