This is going to be a long post and I appreciate anyone who takes the time to read it. I have a 2009 Mini Cooper S with standard stereo. I've replaced all the factory speakers (MB Quart 3.5", JL 6.5" and 6"x9"). All the speakers on the left and all the speakers on the right are connected in series for a ~6.7 ohm load rather than ~1.7 ohm load in parallel. I can change balance left to right, but front to rear fade is not necessary in a cabin as small as the Mini's. I have a Pioneer 10" sub in the rear. They are being driven by a Kicker 400.4 - amp 1 running speakers on high pass and amp 2 running sub bridged mono on low pass. Here is the problem I am having. The amp receives it's signal from the high level speaker outputs from the factory deck and has signal sensing turn on. For some reason we have not been able to determine, there is a huge dropoff in high frequency in the left speakers. Have eliminated the amp as the problem - tried two other kickers and a precision audio amp - all behaved the same. Swapping the high level inputs from left to right still results in the loss of highs in the left speakers. Bypassing the amp altogether and running the speakers off the factory stereo gets the highs back so it is not a speaker problem. Continuity of all wires has been checked and rechecked. I have run out of ideas. The Kicker amp has a fader switch for running off 2- or 4-channel setups - it is set correctly according to Brett from Kicker for a 2-channel setup which I am running. I am using the Mini's front speaker outputs which are full range (the back are high passed for some reason only Mini knows). If anybody has any idea what is happening, please let me know. This has been driving me crazy. Thanks.