ok so ive got a gibson grand concert acoustic with a fishman dual system that has a pickup and a mic ala jack johnson/john butler style. the amp i am running is a 68 fender super reverb rated at 42 watts. i see jack johnson using an acoustic through a fender twin reverb with no problem and john butler goin in to a marshall plexi and they both use acoustics for 98% of their stuff.

here is my problem whenever i plug my guitar into the super reverb it feedbacks whenever its blended with the mic and doesnt sound near as good as how their sound is live. i am wondering if its because of my amp being lower wattage or do they use a certain thing that gets rid of that problem.
i do not want a noise suppressor though. i want a clean signal just like them.
also if i got a twin reverb would this fix my probelm.

Gibson Grand Concert Acoustic
roland AC90

I mean this one time I was jacking it pertty hard and was making noises and what not

You, my friend, are a genius!