Simphony radio W/6 CD changer in my L&K -> PROBLEM

My Simphony radio with 6 CD changer in the trunk on my L&K is giving me some problems with the sound fidelity............Its sound very good in FM Stereo but then the music sound like is in mono. Also if I have the volume hi, then the radio itself lower the sound......Its do the same when I a playing a CD.

This past monday the Dealer install a new Simphony radio and I still has the same problem :( :(

I hear in other Skoda Forum that Skoda has a lot of problem with this Grundig/Symphony radio.

Has any of you has similar problem??? How you resolved??? I dont want to lose the factory look on my cluster so I want to keep the factory radio.

THX,

Isaac