You want to know how the Kickers are wired up. With speakers in the rear I'd guess that he wired them in with the MB Q tweeters on the crossover. I don't think he should do that. You'll want to understand exactly how everything is wired up right now. Then you can start to understand what other options will give you. The biggest part of that (at the moment) is the Kickers because they are the problem and they are being forced into a set that wasn't meant to incorporate them.

I don't want to be negative towards the guy, but if he sold you the Kickers, of course he wants you to keep them in and use them. I think you should exhaust options using the MB Q's only first, and then look at other things. Take the Kickers out and see what you can do with the MB Q's first.

If the Kickers cover up the sound of MB Q tweets, then maybe switch in the Kickers for the MB Qs. There is no point in keeping in a component that doesn't sound good or right. It won't be quite what the crossover was designed to work with, but it should be far closer than having a pair of mismatched tweeters wired up to it. Especially within a confined space like a car, keep things as simple as possible.

Headlights are causing a buzz too? Smells like a possible grounding issue.