This needs elaborated a bit
An actual high flow cat will help lower the exhaust tone. Since he has a Megan cat, which isn’t a cat at all…it’s a test pipe basically…so in that respect it does suck. A good high flow cat can flow almost identically to a test pipe and most certainly dampen sounds a small amount. I run a 300 cell SMSP spun body, FYI. Secondly, low end power would be conserved and high end would will flow more than you need, so ditch the shite one on there now.
In order to cut down on noise…two things need to happen. You can either add another small resonator to the b-pipe, or cut the existing one off and weld in one long 22" one (that’s the longest you can fit under the car and still make the exhaust follow the OEM route). The other option is a CHAMBERED muffler i.e. Greddy SP2, Vibrant stealth, APexi WS, Magnaflow, etc. You current muffler is the culprit right now (exacerbated by the megan junk), straight-through mufflers…with little or no baffling…sound like shit. There are certain straight-through versions that are very well constructed and sound good, like Thermal, Espelir, Spoon, Amuse.
In the interest of cost…go pick up an SNL twin-loop muffler (roughly 60-70$ online…it’s a copy of the ver2 Mugen) and have Jeff weld it on for you.