I'd be *REALLY* suprised if PAC or someone doesen't have an interface for the factory amp to add an AUX input. It's not that uncommon of a request, especially for people with X's that want to add a LCD screen and DVD. In fact, I'd almost guarantee someone makes one.
And if they don't, then it's not going to be too hard to rig up for a repair shop. It's just an amp, nothing special. There are only so many kinds of audio connections in use... even the balanced line stuff is relatively easy to interface with.
All depends on how much you want to pay for the ability to do it..
Drop by an audio store and ask. If they aren't familiar with it, ask them to look in their mobile installer trade magazine, because just about every one of them has someone selling this kind of stuff..
-=RB
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