Hi Robob,
I unfortunately don't have the solution to your problem, but I've struggled with sibilance distortion quite a bit as well, and I have a long thread about it. Maybe some food for thought in it somewhere?
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1245595534&openfrom&1&4&&st0
(Sorry, the sound clips and photos aren't up on the server anymore)
I unfortunately don't have the solution to your problem, but I've struggled with sibilance distortion quite a bit as well, and I have a long thread about it. Maybe some food for thought in it somewhere?
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1245595534&openfrom&1&4&&st0
(Sorry, the sound clips and photos aren't up on the server anymore)