I'd like to get more performance out of my stock 96 cubes without using loud pipes. I know air flow is very important. Am I asking too much?

 

Intake, exhaust, and a cam will wake it up. Not sure if Supertrapp makes an exhaust for the FLSTC, however they are probably the quietest performance exhaust. I'm going the opposite direction, I'm wanting to get a D&D Fat Cat and sell my Rinehart.

 

Take a look at Bassani. I have the Road Rage II. Nice rumble but not annoying on long rides. Without a performance cam upgrade and maybe some new heads and a dyno tune, you aren't going to get a noticeable performance boost.