Mark, I noticed that sibilance in the Aviator as well, and my current center channel has the Vifa tweeter (silk, I believe), as do my mains. With various discs, I've experienced occasional sibilance with them as well.
It's just my opinion, but the higher a speaker's quality, the more revealing it is, and the more important becomes the quality of what's on that little disc that goes into your DVD/CD player. The better the speaker, the more it accurately reproduces what's on the disc. As long as there is no mixing and mastering standard to which each disc must be held, some discs are going to sound better than others.
