Hmm I am surprised you have rasp still. I may sound crazy but you sure they were not put on the wrong? I have the mbrp valved setup with ark. When i had the resonators on it did kill most of that rasp you talking about but made the setup sound far too quiet and almost flat.
I took a video after i got the resonators installed:
Really didn't like the resonators and took them off after a while. After a few months I'd say the rasp is less. I did put on some larger 5 inch tips but those probably didn't change the tone really.
Here it is without resonators when i just got jb4 setup (it sounds killer under boost pretty different than before):
Might just need to give the setup some time. I know that's what also helped reduce some of the booming/tinning interior sound and that rasp around 2k rpm. But yeah I know that rasp you talking about.
Here is a video when I just got it installed with no resonators.