No sound...location of amp

[lebx5]

I have a 2001 X5 with a 4:3 sta nav screen with no dsp. I am having problems with sound i.e. NO SOUND AT ALL. i have shown car to various so called local experts and am getting confliting stories. From their opinions i can see there is a problem with the amp. But there are conflicts in where the amplifier is . Is is amp
a) part of the radio unit under the spare wheel
or
b) in the space below the cd changer & navigation unit in the rear compartment? ( when i got the car the cd changer was missing and there was also a empty space where i told the amp could be)

Any help is much appreciarted

cheers