Honda Blaupunkt no sound other units work

I recently installed a Blaupunkt MP3000 into my 2000 Honda Prelude. I noticed no sound coming from my rear speakers and using the fader control verified this was true. There was perfect sound from the front speakers. I verified there was actually rear output from the player by switching the front and rear connectors. I got sound in my front speakers from the MP3000's rear output but no sound in my rear speakers from the MP3000's front output. I reinstalled my old Clarion CD player and the original factory CD player and with both I got sound from all speakers no problem. With the MP3000 back in, I noticed with the volume and bass maxed, I'd get spurts of sound coming from the rear speakers. The rear speakers in my Prelude are part of what's called an acoustic feedback system. I'm thinking that may have something to do with it. What can I do? Bob Melczarek Dothan, Al.