I've recorded 3 tracks for each guitarist: sennheiser e906, sennheiser MD441 and a Clean DI with my Api 7600 channel strip.
...
what you think about the number of tracks? for metal stuff it's better to mix 6 mics in a clean way o just one mic for side and mix it really hard??
While multiple mics/sources can give a great sound, it's a lot harder to try and get a great sound from scratch from multiple mics simultaneously then it is from one at a time.
I'd try to walk before you run; work on your mic placement and work on it in steps. With those 12" drivers, the difference in sound can matter in inches.
I'd start by selecting which of your four 12s to mic up close. With the git plugged in, turn up the amp volume until you can distinctly hear instrument noise. Make sure No ONE goes near the guitar and blows your eardrum out while you go up close to the amp cab with one ear and listen for which driver is giving you the most defined-sounding hiss. Select that driver to mic up.
Then it's time to select between the 906 and the 441 as the one for providing the main/majority of the sound. Take them one at a time, miking up the selected driver, and find out which one gives you the closest sound to the sound you're looking for. Try (among all other positions) keeping the mic off the center of the dustcap, pointing instead to somewhere around the voice coil, and try it both straight on and at about a 30-40 degree angle in and see which gives you the most desirable sound.
Also, what seems to be needed to be told to just about all new metal recorders; turn down the gain/amp distortion; you need less of it for recording than you think you need when playing live.
Once you have your sound dialed it as best as possible with the right mic, right mic position and right amp settings, then you can start experimenting with filling in tone with the second mic. The options here are almost unlimited, but be open to the possibility that the second mic may or may not actually help. It's not a slam dunk definite either way, only your ears will know for sure.
G.