What are the big differences between stock X-pipe and aftermarket?

I already have the Akrapovic slip on rear section for my e90 M3.

I find it a bit too quiet so I want more sound and have been looking at all the aftermarket X-pipes from: Akra, GTM, Supersprint, Dinan, etc....

Is the primary difference just the removal of the resonators? Reason I ask is I have access to a very capable muffler shop so I was thinking to just let them modify my OEM X-pipe...has anyone else done this?