Just installed the RV6 PCD.

I just installed my PCD this past weekend and there is some rasp going on once I hit 3200 rpm so I'm looking to see what I can do to get rid of the rasp.

My current exhaust setup is RV6 PCD, RV6 J-Pipe and XLR8 Resonated exhaust single tips. I've read around the forums that the MagnaFlow 12640 would get rid of the rasp but would I cut off the XLR8 resonator and replace it with that or would I cut off the piping towards the end near the mufflers to install the 12640?

The Magnaflow 12640 is 6" by 27" long so I'm just trying to figure out how I can fit the 6" x 27" muffler onto the XLR8 exhaust.
https://www.jegs.com/i/Magnaflow/642/12640/10002/-1

Here's some generic pictures of the XLR8 Resonated exhaust that I have as a reference of where to cut the piping.