The resonator is #2 one its under the center console area. Its a straight through design but I could tell a huge difference in sound without it. Before it was put back on I looked at it closely and it just had baffles and packing in it. I guess it just causes exhaust gas turbulence to help with back pressure and sound deading. I would suggest leaving it on and just replacing the rear. I was a little nervous when the body shop cut out the rear areas. I actually had them order a lower black diffuser which they returned without charge just incase they messed it up. The black lower diffuser was $101.00 but thankfully they didn't mess it up.
It can get nerve racking when you are cutting up a car two weeks after you pick it up and to make matters even more stressful its the wifes car and some how I talked her into it all.
I tried to sell her on springs but she told me I am done.
Give me time I will wear her down.