It actually sounds like several different problems. 1. The T&P valve will pop if there is too high a pressure. For residential that is about 150P.S.I. It will pop for too high a temperature. Usually it goes between 210-212 degrees F. The wire wrapped around the T&P would prevent anyone from deliberately opening the T&P for maintenance or any other reason. The valve will pop whether the wire is there or not. 2. The heater could be defective internally right from the manufacturer. I have seen this many times. It can happen right out of the box or anywhere on down the line. Does the heater have dieelectrics between the tank and your plumbing?? If it does check to see if there is any water on or under them. There is one on the COLD and one on the HOT. If they are leaking, the water may be running down under the jacket and appear to be an internal leak. 3. Water softeners and their parts are made largely of fiberglass and plastics. The tanks are robust like a torpedo, but the pipes and jam nuts and fittings are much less so. If you are on city water with high pressure mains the pressure regulator in your house could be hanging up and letting too much pressure into the softener and that caused the plastic parts to break. You didn't mention the T&P actually popping off and you said the heater was only 2 years old so I don't think the heater could have overheated, turned some water to steam, over pressurized the water lines and blew the softener.
I forgot one other thing; most residential water heaters, whether they are gas or electric, have internal HOT and COLD checkvalves in them already, put there by the manufacturer.