Robert, my shop has 36 NTL720 cabinets. Can you post the date code? I have not had the issues you described (but other issues); they have been reliable.
I think EAW blaming on power spikes is lame. The box has universal, switching power supply. I don't run them off AC regulators or surge protectors. Straight off the power grid.
EAW told me to NOT process the signal -- the internal DSPs handle all the low pass and high pass. So can't be passing full-range signal to it either. However, I only use the AES inputs, not analog. AES by design is transformer coupled/isolated, so technically more robust.
The thing to check is whether the HF boost (HF air loss compensation) is engaged. It really cranks up the gain on the high speaker pack.
Having said that, the limiters kick in easily on these boxes. Depending on the size of your space, could a 4 hang be pushing it? They recommended I do 6 per hang.
The two issues we have with them are:
1) The spring-loaded push buttons that release the clasps get stuck. Just poorly designed
2) On some cabinets, I cannot get UNET to work whatsoever. So it's a pain to configure each one via USB.
-JR