Jeez, I really hate to throw cold water on someones enthusiasm for a project.

You asked about easy ways, so I assume you're not really worried about cost. I gotta ask, though, when you've replaced al of the parts you mentioned, plus upgrade the power transformer to provide the additional voltage and current you'll need, what's left of the original, the box?

I suggest the easiest route to more power is to trade/sell the amp you have now, and get a bigger amp. Yes?

If you like the sound of the rig you have now, don't mess with a good thing. Just mic it into your band's PA mixer.