I don't think it can be adjusted. From what I remember, the HK speaker system is the same for both the std and the NAV equipped cars. I know that for the 11 OB (no sure on 12 or 13), the nav equipped cars allowed for additional adjustment of the speaker systems that wasn't available on the std head unit. The rear speakers on mine blow too. As soon as I touch the fader, (no Nav) I lose the rear speakers. They also seem to have a high and low limit cutoff and they only play muddled midrange. I gather this is a holdover from the nav cars and std radio people are out of luck on adjust the fade while maintaining the sub and full range sound. For some reason the only mid and high range speakers in the car are on the dash. The front doors are subs and the rear doors are crippled. This has to do wiht it being a 2 channel system with forward biased sound.can the harmon kardon amp be adjusted? the rear speakers sound terrible and i cannot hear the subwoofer with rear fader on. is this system just for looks on paper, because i know 440 wts with a sub should be alot better.