Muffler selection
Pipe diameter would help. I’m on my phone and I can’t quite tell, but it looks like a 2-1/2 pipe. I’ll wait on you for that.
Adding an X or the much easier to self install H pipe helps by a few db’s. Adding a resignator. (sp?) would help. But if it is the inside where your finding the noise level uncomfortable, that changes things. It can be easy to fix-ish but you may not like how it looks with glass packs before the mufflers after the X or H pipe added in.
(FWIW, the Magna Flow comes in a stainless shell and has a true inside diameter of the pipe size your using. No neck down on the inside.)
The only other thing I can think of is a pressure wave cancellation box after the header, before the X or H pipe. It’s exact spot would need a dyno, engine or rear wheel run, to see where the effects of the pipe length after the header is cut to.
Then add the X or H into glass packs into the muffler. It is a lot and gets dang busy underneath there for sure. This route is a bit more complicated, time consuming and a basic PIA. (HUGE PIA)