I did exactly the same! Here in Brasil, we call 'semi-acoustic' that electric guitars with a resonant body such as the ES-335 and similars. And being a guitar player myself I was puzzled why he didn't just plug the guitar as you do with ANY electric axe! Turns out that the OP is talking about an acoustic guitar with a built in electric pickup.
Anyway, the poor experience I have with acoustic guitars equiped with piezo pickups is that mostly of them will deliver a weak and harsh rusted tin bucket sound when plugged directly to a mixer or similar, unless, of course, you have a super-expensive instrument where only the piezo pickup will cost thousands of dollars. Being the Ibanez AEG a cheap one I suppose that it is not in this ball park and probably this is the root of your problems. If it would me I would forget about to plug it directly and would go for a good microphone.