Well depending on where you live, you might be required to have the cat in for inspection. If the cat doesn't work correctly anymore, you'll probably just have to get a new one. I think the resonator might be too long for that exact spot also.
All a resonator is, is like a first muffler. It should kill my drone/rasp in my exhaust.
You would put the resonator after the cat.
So it's like: Headers->Collector Pipe->Catalytic Converter->(Flange)->Resonator->Pipes to mufflers.
EDIT: I must leave for work now so I may not be able to help you until later tonight. Hopefully this helped explain things more and others can help while I'm away.