Did we sell you kits or did you pick up the parts and build 'em yourself? If you bought the parts yourself, did you get the genuine KSN-1038 or a substitute? And in either case, are your speakers pre-2003 models or if newer, did you install the midwoofer coil? I ask because they can be a little midrange-heavy without the coil. If the answer to any of these questions is "no" then you may find a problem that has an easy and inexpensive solution.

Oh, yeah - One more thing. It's very easy for debris to fall into the tweeter during assembly and I've found that is a common condition with speakers in the field. So you might want to remove your tweeters and take them apart and clean them. Remove the three screws in the back and carefully take off the back panel. Inspect the cone and cavity for debris, and gently blow across them to stir any that might be there loose. If there's any sawdust inside, that will obviously reduce their performance and this process will ensure that's not ailing your speakers.

I don't think your choice to use fiberglass insulation is causing you any problems - In fact, that's the stuffing I prefer. But there are several suggestion here in this forum's archives, and things to think about and try to get the most from your speakers.