Re: Micing techniques for multiple mic's on an amp!
If you can phase reverse at the board, you might try one in front and one behind. Or try one from behind only. It's a delicate balancing act, but it can yield good results. You'll get tremendous depth from inside the cabinet, and then your positioning can affect how much of that low end woof from the cabinet gets into the mic head.
You can also try one dead center, about twice as far away as the cone is deep. So say the speaker cone is 4" deep from the face of the cabinet, you'd be 12" out from the center of the cone, but 8" out from the front of the cabinet. You want to be far enough for the lows to come out from around the perimiter of the cone, and disperse to the center position. Too close, and you are just getting the sound of the paper at that location. There might be a sweet spot for you on that paper somewhere, but I imagine you are wanting a sound closer to what you're hearing from in front of the amp. Close micing is great, but for what you're describing, I'd suggest coming back like that.
If you really wanted to get nuts, you could pry the head/diffuser off, and stick a foam pop filter on it.