So are you trying to tell me that the only reason exhausts make more or less power is because of the mufflers? LOL.
Usually, an aftermarket exhaust WITHOUT tuning will make around the same number, give or take, as it would without one. If you are unclear on that, you probably shouldn't hand out "advice" to people that don't know these things. And if he is going with higher boost levels, it is indeed best to go with a different intercooler and TB hose. Depending on how long the stock one holds up, it would also be smart to run an aftermarket BOV also. A stage 2 tune on an AP is primarily meant for strictly TBEs, nothing more, nothing less.
It is necessary to abide by the recommendations specified by Cobb and/or your tuner because with each and every part of your power train you install, there is at least a small difference in the way the ECU will recognize it. Different things such as air and fuel mixtures as well as scaling and duty cycles will need to be altered to compliment the new parts. Hence why even the slightest difference can make your car's idle "dip" in circumstances like coming to a stop.
He can run the stage 2 map with those parts if he'd like. But that's up to him to risk his longevity. So if you are not familiar with why it is essential to stick to the right parts in accordance with the tune, please do not offer a newbie advice. Thanks.