Actually, to be honest the amp does not sound even remotely like Vai's sound by just plugging in. He's got a lot of other stuff going on that gives him his sound. I'm not saying you could't get a sound close to his...just that it doesn't sound like that out of the box.
The beauty of this amp is it's versatility. It is a lot less harsh than say, a Marshall. Great clean sound. Very warm lead tones. Of course, a lot depends on your settings. I would imagine you could get a great clean jazz sound. I can get just about any tone I want from this amp with the aid of an overdrive pedal and delay box