I'm no expert, but using the mic-in, as such, should not be a problem, if the gain is set appropriately. Both guysonic and DSatz measured the mic-in overload point at ~ +2 dBu. At 10 mV/Pa (according to the AT spec sheet, although SP shows 8 mV/Pa), you need 134 dBSPL to generate that voltage. As a point of reference, a trumpet is ~ 130 dBSPL at a half meter. We're talking threshold of pain levels. Turn the gain to 2, and you will probably never overload unless you have very sensitive mics or are on top of a stack. Of course, the line input gives you a wide margin of error, but you will generally have a hard time overloading the mic-in with the right gain setting...