With all the mids not working, it would seem to me to be the stock amp, whether it be bad or a fuse. The car is now 8-9 years old, so it could be speakers, but not likely. A 750 typically isnt going to be owned by a kid that would blow up the stock speakers. I would start with checking power back at the factory amp. The "radio" fuse is typically for the indash piece and the amp is fused either at the amp at a different fuse location than the "radio" fuse.
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