4 mid speakers all cut out, blaupunkt, freelander?

I have a freelander xi millennium with blaupunkt 9 speaker set 1 x woofer, 4 x tweeters and 4 x midrange. the mid range started to cut out intermitantly then about a week ago cut out totally, as all of them cut out at the same time I believe its a connection issue. I have tried a seperate working head in the vehicle and the same prob is noticed so its not the stereo, there is an amp under the front passenger seat that powers the speakers. Any ideas?