mufflers vs resonator
Actually, a resonator and a muffler have the same function, but are really different in the way they work. A resonator is basically hollow, on my stock 1990 SC, it has 2 inlets and one larger outlet. The exhaust gases "collect" in a rotating pattern (resonate) inside the resonator, hense the name. This gives the initial back pressure in the system (VERY little) just enough to change the tone of the exhaust. The SC is considered a luxury sports car so the makers designed them to be quiet, yet fast. By changing the tone, it removes the initial "popping" sound a V6 makes if you were to run only the headers off the block, allowing for the mufflers at the back to finish off the job a little easier.
The mufflers, (stock has one at each tailpipe), are designed externally like the resonator. Difference is that mufflers use internal fins to allow the exhaust to flow a certain way. That certain way makes the gases difract, resulting in the interference of the sound waves given off. When waves interfere, they cancel each other out, or become "muffled". This involves a little more back pressure than the resonator.
Remember: some back pressure is useful when running in cold weather because when the supercharger forces the air into the cylinders, on a 6-cyl engine there is always at least one other cylinder on the opposite exhaust stroke, while another is on the power stroke. This balances the momentum swing in the crank and flywheel, offering a smoother running engine, which in turn is more fuel efficient and quiet. This is also why head gaskets are blown when the exhaust is not opened up more before adding boost. The designers of these cars built them to withstand an equilibrium limit or an exhaust:intake ratio. You are on the same line I am, currently to upgrade the exhaust system on our cars, but I still want to be careful not to fully eliminate back pressure or else the fuel running will be getting pricy. Good luck and hope this helps.
Also thanks to Thomas for the helpful advice on my exhaust journey.