You took what I posted a little out of context. I didn't indicate garbage tweeters in Jensen speakers would compare in any way to a good metal, ceramic, or textile tweeter. I am also not saying all tweeters sound the same. However, the x-over and room accoustics will end up being the controlling factor in how a tweeter will sound. If the tweeter itself is linear then the x-over can be formed to produce whatever sound the manufacturer may desire.
"Are you using titanium tweeters? It's fairly common with those and could be an issue with being crossed over a bit too low." was in my first post, so we agree on the crossover being a possible cause. I mentioned the Ti tweeters because I have heard this from them in several cases. I'm not sure where the reference to the Jensen tweets came from, but I have heard some of most types sound bad. I may have been assuming that the room had passable acoustics, which I admit, may be a stretch since it's the most neglected aspect of almost all of the "music or HT" rooms I have been in. This being the case, a room that is too refelctive is a likely candidate, so we agree on this, too. Any equalization, if used, can be a factor, too.
Sibilance from a speaker system is inexcusable when the room and EQ aren't factors, IMO.
Our differences in stating our opinions of the cause aside, it's easy enough to find out if the acoustics is the problem. Turn the speakers so they aren't firing directly at a hard surface, reduce the volume and move closer to the speakers. If the sibilance is gone, the room is too reflective and if it stays, it's probably a crossover, source material or possibly an EQ issue.