I installed a Nakamichi CD400 headunit in my 2004 Disco SE. I purchased the wiring harnesses from Autotoys. I have connected the line level outs from the headunit and switched the internal amp on the headunit off. The sound from the rear sounds good, however the sound from the front only seems to come through the tweeters. Is there an adjustment at the amp to correct this? What could the problem be? Any ideas for a solution? Thanks.