3 single 2 ohm VC subs in parallel will be .66 ohms, 2 of them in series and then those 2 and the other in parallel would give you a .8 ohm load. 3 of them in series will give you a 6 ohm load. Unless you have an amp that is .5 ohms stable, (unlikely, unusual) your only option is to run them at 6 ohms or you will likely damage the amp then the speakers as a result. You have to remember, anytime you parallel a load, it results in a lower summed resistance lower than the lowest denominator in the circuit. With 3 drivers and a 1 ohm stable amplifier, you want three 4 ohm drivers in parallel which will give you a summed load of 1.33 ohms.
You then take the total output of the amp at that load and divide it by the number of drivers to get what they each get. If the AC units come in 4 ohms, that is the way to do this. At 350 watts RMS a piece, your total amplimer output should be around 1100 to 1500 watts, 1500 being preferable to allow for more conservative tuning which also allows for other factors such as impedance rise and dynamic headroom. That's optimal and should you end up with 750 watts, still acceptable as the difference between 750 and 1500 watts is 3 db (33%) in volume to the ear. The difference between 750 and a 1000 watts is almost imperceptible.
