Hey Mike, How many watts per channel does your Sony have? What is the brand & model number of your speakers? How old? Are they 8 ohm speakers?What kind of wire are you using? How long? What is the gauge? Sorry for all the questions, but its important to narrowing it down.
If your Speakers are 4 ohm, this could be the problem. Of course, wiring problems or shorts could certainly cause it. Are your Speakers efficient? ( how much power is necessary to drive them?). When you crank it to +45, you are in he upper range of what power your receiver can put out. More speakers are damaged by amps that do not have enough power then too much power. When the amp runs out of power (at peak nano seconds;) especially bass, the amp goes into clipping. Clipping causes speakers to blow, amps to blow, etc.