Amplifier problem with Volvo 2003 Volvo S40

[babs_fleming]

My daughter bought a 2003 Volvo S40 in April. About two months ago, it appeared that one of her back speakers wasn't working properly. After having it looked at by the small dealership she bought it from - they said it was her amplifier. The radio only works with the front speakers and has a terrible tin can kind of sound. We've been told she can't replace the amplifier any other way than through a Volvo dealership. They want to diagnose the problem first ($125 or so) and then if that's the problem, they will fix it for around $250-$275. She's been told that it can't be fixed by a store that sells car stereos and such because it's all fiber optics. Is this true? Is there another way we can replace the amplifier that won't be as expensive? Thanks for your help.