keep your ALL your cables away from each other. Don't lay AC across speaker wire on let AC cables get near interconnects. This may help and costs zero dollars.
It's most probably the speakers and room-reflections related.
I have spent a lot of money on these (bogus) cables/filters products and they don't help on the long run.
At first you imagine it is better but then the sibilance is back.
I solved mine with the digital room correction and a few absorbers, I had a peak from 4 to 10khz when checking the measurements.
Thanks all for the response. I have considered this to be a room issue. I do use some asc panels up against the large picture window behind my listening position. It helps...but not im in a nyc apt. and am very limited in space and ability to put up anything on the walls permnantly.
The t issue is something im curious about. For no other reasons then space in my audio cabinet i was considering an audio magic stealth mini. The monarchy audio regenerator seems to be interesting as well, but dont know if i have room height wise on my 6 inch vertical shelf.