SN95 Exhaust Questions

Ok I'm wanting a little more low end rumble type sound in my 94 GT. I've been pretty happy with it for years but after seeing all these YouTube vids of exhaust it's making me want more. Lol

Right now I have the stock headers, stock h pipe with cats removed, not gutted. And flowmaster 40 series. I like the sound but would like a little louder and lower tone. All suggestions and comments welcome! Thanks!

How much difference would an aftermarket H pipe make?

I've read several times that aftermarket headers aren't worth it. Is this true?

And as far as cat back goes, how much difference is there between one from a local muffler shop and all the expensive setups?

ok thanks, I do like and want to keep my 40s I looked up the mandrel thing and that makes since. So, one more question. If i keep my flowmasters and stock headers for now. And get a 2.5 inch H pipe and tails. Esentially making it 2.5 all the way the way back instead of 2.25. how much difference in sound will that make?