Any reason why my audi A4 wont accept aftermarket speakers?

[JDM82]

I took my car to a very good audio centre, Autosounds Newcastle to upgrade my original speakers in my Audi A4 convertable. The speakers suggested where FOCUL.

The rear speakers went in no problem but they couldn't install the front ones. Something to do with the crossovers not working???

They said they have never had this problem before and it could be a 'hidden' amp or something that Audi have fitted that they don't know about. They checked behind the dash and in the doors etc. The speakers worked on the bench just not in the car?

Any ideas would be great.

[Rhyso]

Its not fitted with a Bose stereo originally is it?  Perhaps something conflicting with that as that has a few extras like a sub and an amp 

Shot in the dark really