Correct. If you have a cat back without the resonator, you will not like it. It's still loud with the resonator and a cat back, but not deafaning. Maurice put the stock muffler (cat back) back on and it's very quiet.
Once again, the high-flow cat is not there to increase HP (it -may- add a few or it -may- take away a few). It's there for Stage 2 so you don't melt the stock cat. It can handle higher temps than the stock cat.