Keep in mind that tweets do not need very much power at all to get "loud", also you said you had it at 4000hz, if you are boosting or cutting at 4000hz the super tinny crazy loud part will be higher than that and you are doing nothing to fix that. it sounds to me like you are a little in over your head with the amount of adjustment and additional components you have at your disposal. Go back to basics. no boosting or cutting, simply one chanel of power going into your passive everything set flat, no additional caps/resistors... speaker wire going to your tweets and mids from the passive crossover that is set all flat. make sure you head unit is set flat, and that there is no processing at the head unit, the loud button is off. make sure the amp is not processing the signal any, other than low pass to protect the mids. Start with your head unit set to 50% and the gain of the amp at 0, then advance the gain to the point where the tweet is comfortable to the ear and fairly loud. At this point is it over powering the mid? if so use the cut feature of the passive and cut it 3db. is it still over powering the mid?... I can go on from here if you still have issues. but unless you have the tweet right at the top of the A pillar next to the roof and 18" from your ear, you should not be over whelmed from the tweet. You may have to detune it a bit, cut some of the higher frequencies to make it sound a bit more natural, but is should not be "killing" you