Aux input on 600T MKII Alvarez

[Dejahn.com]

I just found out about the whole aux input mic thing. I experimented with plugging in a lapel mic, but I think I have to get a different cable out to the amp. One with three rings? Someone gave me an acoustic preamp with these two knobs that say they control the two pickups (aux and piezo). And of course the eq on the guitar itself has a seperate knob for each pickup.
Before I go buy another cable, is there a hack to test the lapel mic in the aux port?
Thanks

Oh yeah, this is my first time on any kind of forum. So tell me if I did it right or wrong, okay?