sibilence....any cures out there?

Before you get too carried away, do the positioning thing. Then try different speaker wires. I was surprised with relatively inexpensive speaker cables from Ultimate that took over from the very cheap temporary ones when I had moved and required extra length. Solved a sibilance issue that I was convinced was the room.

Do you use a tube preamp/amp? If so, the brand of tube can have an affect. In my system Sylvania is too sibilant. I sold the Sylvanias to a guy in town - his system is darker sounding than mine - and the Sylvanias were a great match. He said he was hearing details he had not heard before and loved it.

Also, in a friend's system good, high quality copper speaker cables sound great, but when we put silver cables in the system it was extremely sibilant. But like mine, his system is very transparent.

From my experience, Nmmusicman's advice applys to all speakers and all systems. I would add noise caps and RF blockers. I would specify at least two power conditioners on different circuits. I would and do place big bricks on my power conditioners since vibration is also a factor. Low humidity is another factor which is diminished by Spring (static electricity). Get rid of RF and AC noise, vibration, and static electricity and what do you have left? Music if you are lucky.

Its time to upgrade.

Don't believe it. Tweeking is fun and worthwhile.