Loss of radio volume C70 T5 >2006

[0006Andy]

I still have the display and tuner works but not hearing anything through the speakers. How can I establish whether it is the radio unit in the dash or the Amp I the Boot?

I have reversing sensors fitted by the dealer when new, this beeps as it should. does this use the amp or is it separate speakers?

Spoken with Central services who do radio repairs and they say that they cannot test volume function on their workbench, it can only be done with the car, is this correct?

If cannot be fixed, I will need to consider an aftermarket radio, but need to establish whether it is the radio or the amp.

Thanks in advance for any hints tips and information.

For your information, The unit I have is a 6 cd multichanger model number:
34W466M/DZ-6CDIAM.

If I need to purchase an aftermarket radio, any pointers would be very helpful as this would have to integrate into MOST