Problem with Car Audio while playing a CD?

I bought a very expensive CD player for my car---a panasonic---and had it installed yesterday. When i got in my car, everything worked and sounded perfect---except that i didn't have a cd on me at the time, so when i got home and put a cd in my car---i lost the majority of my car's audio. When i turn it on Sirius or FM/AM--my car sounds normal, but when i play a CD---the car's audio decreases to the front basic speakers. I've read the manual and i have adjusted the audio from the actual cd player--i need help!