Stumped!! Changing A3 (8L) Bose Symphony stereo

Hi all, second attempt at posting it in the right place!

Wondered if anyone can shed some light on this problem i have.

I have an old A3 8l with a double din Symphony Stereo, bose is written on all the speakers and I have the nice plasitic sub in the boot with bose on it. So i decided to change the the unit for a JVC so i can play Mp3's etc. I got the PC9 - 408 cable to make ( so I thought) my life easier. Put it all together, new stereo comes on fine but no sound.. Nothing!! I can attach the blue/white cable to the speaker outputs from the unit and I can hear the sub kick in.. and thats about it!

I have also tried the pc9-404 to test with the line outs but still nothing! Am i being that dense that I cant see right in front of me that im doing something wrong! As soon as i plug the old unit in all the speakers are working.

The only connections I have coming from the car are power and the 20 pin connector with the ariel and the ground.. and one other with the tel mute.

Thanks for your time..

Okay.. im a numpty!! Just sat here after finding this site.. and read all 51 pages of posts.. and THANKYOU Andymac you are a star.. after reading about connecting the blue/white wire to the remote on the JVC in another post all is well in the world !

Now going to hide my head in shame.