I think the biggest problem for Gibson's amps was simply lack of appeal. Gibson are known for their historical guitar designs, not their amps. Anytime someone's got $500 or so to drop on an amp, they're not going to try that unfamiliar Gibson over in the corner when Marshall, Fender, Mesa and about 15 other brand names are vying for the almighty buck. The image I always had in my mind about Gibson amps was little combos you might purchase to go along with your new Les Paul Special back in the 60's. It's just the way I always pictured them.