either wire the VC's of each sub in series, then the subs in parallel or wire the VC's of each sub in parallel, then the subs in series.
i think the first set up is reccomended though
hmm, lets see here. If you series the voice coils each sub would be 8 ohms, combne those subs in parallel and your back to 4 ohms. If you parallel the voice coils to 2 ohms each sub, then series the subs together, you get 4 ohms again. So, you are royally SOL! 2 ohms cant happen. You could however, get a 1 ohm load, but i would have serious doubts in my mind that an audiobahn could drive a 1 ohm load without turning into liquid chrome. Get a better amp.