Don't know much about the green filters.. tell me more. brand etc...
As far a muffler. I have experienced the same with my 400E. I installed a stainless twin tipped magna flow. very quiet at idle. slight rumble under normal accel. hard accel and high rpms and the car sounds great... refined grawl. I like it...
I was told that a sure way to give the V8 more Beast Like sound is to bypass/remove the center muffler. Those giving me that input said, "brace yourself, getting rid of the center muffler will prodce a drastic change in sound". I wasn't game for that but something to consider if you are looking more a more pronounced exhaust sound.