I have a Denon AVR587 running in 7.1. I have an unusual problem as the rear channels seem to play all sounds at a higher pitch and lower volume than all the other speakers on the system. I am using a voice matched set of Polkaudio speakers and they all sound the same on the front and center channels so I have ruled out a speaker problem. I have also ruled out a wiring problem as I have been over it several times. I have done every adjustment that I know of and the rears still sound very different, almost a tinny sound, even with the test tone. Does this sound like a problem with the amp and if so, how hard would it be to fix?

Rear channels will always have less sound volume and also less frequencies.
1st set their size to big to increase the frequency range sent their way.
2nd tell the amp they are a lot further away than they really are.
3rd up the volume level on the rear and lower the front and middle.

this should trick the amp enough to make you happier.

Hey ajn1n1 we need to fine where the tinnyness is coming from Lets do a test shall we,

hook up your voice matched polks to your front left and right speaker outputs on your amp to see how they sound as mains. if you hear tinny then its the speakers. sometimes speaker need to be broken in a bit.

hook up your main front left and right speakers to your rear outputs. if you hear the tinnyness then its the output of that channel on the amp or a setting. Newer amps let you change speaker sizes in the menu so that it can change over the crossover for that channel.