Years ago as part of a project we had with the Motion Picture Academy (or whatever it was called then) I was invited backstage at the theater where they screen for the awards. The speakers were setup to fire through the screen.
At least Stewart makes such screen in sizes suitable for HT, and there are probably others as well. This would seem a possible solution for those who insist on a center channel that matches the mains exactly. Not sure how the sound is affected by these screens. The screen at the Academy seemed very porous, but I doubt you could get away with that at the close sight distances of an HT.
Incidently, a foolish colleague had convinced someone at the Academy that our famous reserch institute could bring technology to improve the sound of their films. Of course he only priced himself into the contract. My role, as an expert in psychoacousitcs, was to size up the situation and try to assuage a discontented client. A meeting with the technical movers and shakers of the studios soon convinced me they knew far more about movie sound than we or anyone we were likely to bring to the task did. Of course we had world famous acousticians, physicists, and chemists, but not with expertise in sound for movies, nor was such expertise priced into the contract. My advice was to waive all charges, terminate the contract, and appologize. That's what we did.
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