Can sibilance be eliminated?

I've found the worst of the sibilance can be decreased or eliminated via careful controlling of room reflections and power conditioning.

Some questions & comments:

Why would you completely want to remove all sibilance? It is a natural byproduct of certain vocal output and occurs fairly often in "real life". Probably the base-line here should be to set expectations correctly - if the sibilance is accurately recorded in your program material you probably want it accurately reproduced - no?

Next, are your speakers properly set up & calibrated? That's the first thing to attend to. Sibilance reportedly/typically occurs in the 5-10KHz range, so if your speakers are peaking in the upper ranges (including maybe even higher than 10K) that could contribute mightily. That's probably the #1 thing to check out.

Room (reflections, etc.) is probably next. Since your speakers are what makes the sound and the whole room environment (including speaker placement) is the next-most significant thing that affects what sound(s) reach your ears then that's the next place to focus. Little things, like "is there a flat-topped coffee table between you & the speakers?" may contribute significantly to what's reaching your ears in your listening position. You can find a wealth of material on room factors at Rives, etc. that may help.

If you plan on keeping your speakers, etc. then all that stuff above is the stuff that matters most. Cables and power cords and conditioners and all that other "stuff" have such an infinitesimal impact on the sounds you hear, when compared to speakers & room environment & source material, that you can pretty much de-prioritize those things until you have your speakers and room tamed. As usual, JMO & YMMV...

As others have said, most sibilance is in the source recording. Different types and brands of microphone produce recordings that are dramatically different, and some are better than others with regard to sibilance.
Try playing back the record at reduced volume level. Problems caused by your playback system will generally increase with volume. It the problem persists at all playback levels, it is probably in the recording.

Marakan hit the nail on the proverbial head. Audiophiles are gladly ignoring that the chain starts with the recording and that they actually have very little control over many aspects of the sound reproduced by their system. Mr. hosehaed is also so right in his statement that sibilance is, often enough, part and parcel of a singers instrument and delivery.

To the best of my knowledge, sibilance is used to categorically describe a certain type of sound ie a hiss, whistle, s, sh, and in the case of audio, perhaps including certain sounds that certain cymbal strikes make or perhaps sandpaper blocks.

There is nothing wrong with sibilance in one's system or speech. The problem is negative sibilance ie where an 's' is now pronounced as 'sh'.

Assuming the negative sibilance is not in the recording, based on my own experience, I would attest that negative sibilance is entirely based on the quality of AC electrical and whether it is purified and/or conditioned.

A reviewer/columnist who evaluated my system last summer noticed immediately that there was no negative sibilance and he inquired about my passive line conditioners.

In addition, as an experiment about a year ago, I removed only my amplifier's dedicated passive in-line conditioner and installed a 20amp Hubbell IEC connector at the end of my 10 gauge 6N OFC solid core romex. The romex was connected at one end to a dedicated 20amp circuit breaker in my service panel and the other end now plugged directly into the amplifier.

Among other negative effects induced, the most prominant was negative sibilance. And this was noticeable within seconds after making the switch. Upon switching back, the negative sibilance was gone.

Therefore, at least in my experience, I feel confident quite stating that negative sibilance is induced entirely by the noise generated in my AC and without my line-conditioners.

-IMO