I will take a pic next time i go into the shop to discuss. I should have done that to begin with actually.
They synopsis is this: From the OEM headers(x2), it is a 2-1/4" pipe. This feeds into your secondary catalytic converters, back to 2-1/4" pipe (x2). These two pipes feed into your resonator. The resonator is a single-out 3-1/2" molded pipe. This feeds to your muffler. The muffler then outputs (x2) 2-1/4" pipes [stock]... and if they came with fancy tips, they basically just slide onto your piping and welded.
My suggestion is that if you want LOUDER, go with just sticking a y-pipe onto the molded 3-1/2" pipe and out to make your quads. If you want quieter, then go with the muffler of your choice that has 3-1/2" in, to (x2) 2-1/4" (or 2-1/2") out to make quads.