xPETEZx; Well as you see in my posts above I was able to RMA just the amplifier.
They did want me to test and make sure it really was the amplifier though. (I.e. bypass it as I described above in the picture)
That is very understandable though, cables often go bad, especially in the doors hinges where they are routed through and thus move every time you open the door...
Or via the crimp connections which are done by the person installing this kit (I opted to solder my cables instead for this reason)
Actually I have a friend with a 325i just like me but stock HiFi system, his drivers side speaker is too cutting out.
Probably cable or speaker problem in his case...