Sound Stopped coming from the Speakers all at Once

Hi there,

I have a 2002 xterra with an after market sony XAV-AX1000 head unit and am having the problem of no sound coming from the speakers. The two rear speakers were both blown when I got the car and so I have always just used the two front door speakers and A pillar tweeters to play music. However last night when I accidentally activated the rear speakers through the balance/fader options, there was a loud distortion sound and then silence. I was playing music at the time. I have checked all the fuses that are related to the audio and replaced one that was blown labeled electric plug. The rest were ok. The car does not have a factory amp or aftermarket one and so the speakers relied on the small amp which came with the Sony head unit. I had initially thought that this may have been the issue but I took the unit out this morning and the fuse was ok and I even tried the factory head unit too, but no luck. I had thought that I must have blown all the speakers at once, but everyone online says thats quite rare. Also the Sony unit still turns on and works just no audio. Any ideas? Sorry this ones a long one.