I'm trying to locate amplifier for sound system. I looked at the diagram and it points that it should be installed in trunk close to CD Changer. I found CD Changer, but the other side of the bracket is empty. No spare wiring or fibre optic cables also found.
I looked under front seats, nothing there as well.

Does anybody have any idea?

The amp is indeed in the trunk by the CD Changer. Pull the left side trunk liner and you will see the amp on a mounting bracket. Follow the fiber optic ring and you will see it.

I've removed completly trunk lining. I'm not blind. I traced fibre optic wires and found that they go from CD Changer into behind back seat. Then I read about COMAND 2.5D (that I have) and found out that these kind of systems have built-in 4 channel amp.