Ehh, I wouldn't say that-as a matter of fact, I'd straight out disagree...I've seen it a few times where complete new free flowing exhaust required new jetting, whereas your factory fuel injection system will use adaptive strategies to figure out what fuel injector duty cycle to use based on the exhaust O2 readings under all sorts of different throttle and ambient environmental conditions--EFI is cool that way.
All that being said, again, I'm not trying to convince you one way or the other...just giving some perspective.
X pipes can be a help, and usually smooth out the tone in the exhaust.