If the chip has thermal and short circuit protection (which it does, according to the datasheet) then it seems the only way to fry it is too much supply voltage or a gigantic input signal.
Really, the best way is to find someone with an oscilloscope you can borrow to see if it is oscillating, check the level of your inputs, and perhaps your power supply quality (does it have a high ripple?)
Since your transformer is close to the maximum supply voltage, try building a regulated power supply. So transformer, rectifier, filter capacitor, and then a regulator IC and some more filtering. If you have a double-ended supply (i.e., +/- 12V) you will need a negative regulator IC as well. Both regulators should be adequately heatsinked and capable of supplying enough current. Design the regulator circuits to give you a DC voltage within the operating range of the amplifier (the datasheet will tell you how to set the regulator's voltage), and check this DC voltage before you connect to your amp.
However this is a complicated solution which could potentially introduce more problems that will be hard to solve without a scope. Do you have access to a regulated lab power supply? You can use that to test.