I have a 2016 flhtk with a 110 Se big bore stage 3 with head work done on it and it produces 120 torque and 106 hp with a fat cat 2 into 1 header with a fuel moto slip on. I also have a set of S and S 2 into 1 into 2 header pipe with CVO slip ons. I require exhaust that meets regulation for noise but the max performance. What do you suggest, I do not want to buy a new head pipe.

 

Look at Supertrapp slipons. They have discs in the end caps that can be added or removed to adjust the sound level.

 

I like V&H Monster Ovals. Max torque in a quiet package. I liked them on my '03 and purchased monster rounds for my '13. I like the monster ovals best.