I wouldn't say the axles are weak, though I have broken two.
It is a force exerted by the crappy mounting of our rear differential cases. The case moves too much, putting a LOT more pressure on the axle at the dif.
A 2-step wouldn't lead the axle-breakage. Think of it as one less thing to concentrate on when launching (at the track). For me at least, I can't hold the gas at a certain RPM for too long, as I like to focus on my footwork and the lights or countdown. With a 2-step, just hold the gas down and it will hold the RPM at w/e you set it to,about 5k RPM in the Speed6 should be fine. Now, all you need to do is feather the clutch at the right time. Remember once you let go of the clutch, the 2-step (the '2nd' step) comes into play and you will approach redline.
Just my way of looking at it. MSD makes them, but I don't know anyone myself who has installed it aftermarket yet. My buddy has one in his garage waiting to go into his S14.