Marko, Iam no expert but I think your problem is your head unit. I have a 1999 c230k and my son drove the car for a while and he put 2 15's in,and blew the rear window out of the car,then he went to 1 15 and it was still too much, they were Image Dynamics sub's, and I think the amp was 1000watt jbl.and pioneer mp840 head unit. I now have a Image Dynamic 12', with a 300watt zapco amp and it hits hard. I do not think that your stock head has the adjustablity for what you need,or something not hooked up right. check the leads at the amp and sub and make sure they are tight. Good luck.Ross