Audi A8 from 11/1998 and TV Tuner

Hello,
I have already built in my thick a tv tuner. at this is also aux entrance (video and stereo audio). Is it so that this entrance sounds particularly bad? if I have a mp3 player that is very well connected to my system at home I hardly have to go up, but hardly in the middle of it all the more in the middle, that sounds naturally uebel. have you made similar experiences ? or is it
but at the player and the wiring ?

griss Stefan