hy people i have the following problem. it's about the speakers. when i installed the unit, i had a great sound. 2 original speakers in the front and an old stereo system in the back. the car is a vw t4. t4. had to reconnect the permanent cable. since then i have too much treble or the bass is overloaded. also the sound distribution front/rear is hardly adjustable. what am i doing wrong? i have already reset several times. i can't even get a basic setting right.