I don't have to worry about having an air pipe on the cat b/c the air pump opens the ports correct?

 

right
well, as long as you have either a straigh pipe or the cat gutted. if you remove that pipe but keep the stock cat, it will melt without the oxygen fromt he air pump

 

On your S5 - yes.
When my prior NA's air pump bracket broke, I ditched the pump, blocked off the ACV, and hooked up an electric pump the work the aux ports & VDI.

 

Is that all cats or are there certain brands that won't melt under rotary heat?

 

Part of how a multi-stage cat works is that the first section processes part of the mixture, then with the air from the air pump, the 2nd stage processes the remaining mixture.

So if you remove the air pump, it tends to clog of the cat, because effectivly you have shut down one whole section of the cat.

As soon as the cat is clogged, then the cat melts down because of the force of the exhaust.

Now Mazda and a few other High flow type cats will hold up to the heat longer than the $100 ebay cats, but they all will tend to fail prematurely with the last part of the cat not getting air.

 

basically all cats and glasspacks.
if you want to keep it quiet, try this in place of your cat:
http://www.racingbeat.com/FRmazda2.htm

 

I have to pass emissions testing. I'm not trying to remove the air pump by any means at all. I am just trying to think how I am going to do an exhaust. Should I try to run true duals with a cat for each pipe and a splitter for the air pump hose to run to each, or should I go single with something like a bonez? BTW, I don't know my car exhaust's current condition because a previous owner welded a cat in without a passage to the air pump hose, so I can't find it, I'll have to go look for it tomorrow.