Well technically yes, you can stack defiance from a single power. HOWEVER, the amount of time you have defiance from a given power is just slighty above its default recharge value, so you're not going to be able to stack it more than once. And plus, setting an attack to auto isn't going to be very beneficial unless you're slotted with enough recharge to make the power "perma" (ie, if can fire off again as soon as it's done animating).
it's best to "chain" your attacks. Click one, and while it's going, Clik another power to queue it so that it goes off asap. And when THAT power is going off, click another (the first probably won't be recharged in time to chain just 2 powers)
As for DR, i don't think it applies to defiance, but blaster damage got pretty gutted anyway, so mweh.
-STEELE =)
Allied to all sides so that no matter what, I'll come out on top!
Oh, and Crimson demands you play this arc-> Twisted Knives (MA Arc #397769)
Can defiance stack off the same attack like using flares over and over? Is their DR for it stacking in PVP areas?