I have a MTX 6304 amp, the rear channel has barely any sound and is distorting horribly. Any advice?

YOU MORE THAN LIKELY HAVE A BAD CHANNEL ON THE AMPLIFIER THAT HAS HALF-WAVE OUTPUT, CAUSING THE SERIOUS DISTORTION. USE THE PROCESS OF ELIMINATION. SWITCH THE RCA INPUTS AROUND AND IF THE PROBLEM STAYS IN THE SAME CHANNEL, THEN THE AMPLIFIER OR SPEAKER IS AT FAULT. IF THE PROBLEM SWITCHES TO THE OTHER SPEAKER, THEN THE PROBLEM IS THE RCA CABLE OR RADIO ITSELF. YOU CAN VERIFY YOUR FINDINGS BY STARTING WITH THE SPEAKERS FIRST. SWAP THE SPEAKERS AROUND AND IF THE PROBLEM STAYS ON THE SAME SPEAKER, THEN THE SPEAKER IS AT FAULT AND IS PROBABLY HAS A SHORTED VOICE-COIL. IF THE PROBLEMS SWITCHES TO THE OTHER SPEAKER, THEN THE AMPLIFIER OR INPUTS ARE TO BLAME. BY FOLLOWING THESE TWO METHODS, YOU WILL BE ABLE TO DETERMINE EXACTLY WHICH COMPONENTS ARE AT FAULT. REMEMBER, YOU HAVE AN INPUT, AN AMPLIFIER AND A SPEAKER. THIS PROCESS OF ELIMINATION WILL HELP YOU IN THE FUTURE WITH MANY TYPES OF PROBLEMS. LET ME KNOW IF YOU REQUIRE FURTHER ASSISTANCE.....V
PS: MAKE SURE THAT THE GAINS AND BOOST CONTROLS ARE SET TO THE SAME LEVEL FOR BOTH CHANNELS BEING TESTED. ALSO MAKE SURE THAT THE BALANCE CONTROL ON THE RADIO IS STILL SET TO THE MIDDLE. DON'T WANT THESE CURVEBALLS INTERFERING WITH YOUR TROUBLESHOOTING......V