First, you can assume that anyone who questions your definition of yourself (fringe high-end, sensitive ears) based on what equipment you own has deeper issues and displays their own ignorance by making such a tenuous connection (IOW, consider the source). If it sounds right to you, then it's right for you, period (ignore them). Also, we can only assume that you are indeed such a person. If you were not such a person, there certainly would be a low probability of you merely thinking you were such a person. Rest assured, Phil, the rest of us are with you; we'll begin by not questioning your premise.
I am a fringe high-end audiophile cursed with really sensitive ears. Let's not stoop to the cheap shots and focus instead on solving an issue.
I have a new HR24-200 with a severe sibilance issue. Connecting the HR24-200 to the Samsung 650 series TV via a BetterCables HDMI cable...Has anyone else noticed this extreme exaggeration of SSSSSS sounds regardless of channel from the HR24-200? If so, what did you do to eliminate it?
I will say this; your ears are not so sensitive or golden that you are imagining sibilance or perceiving it where the rest of us just don't. You do have a real sibilance issue here. That you may have sensitive golden ears is really beside the point; it just makes the fact that there really is sibilance that much more annoying for you, likely.
Sibilance. There are really two definitions; one would be an unusually higher frequency peak in the "s" and "z" consonant range of human speech, compared to the rest of the band. The other is actual distortion at that frequency that sounds very similar, because there is a lot of aggregate energy from the distortion that manifests directly at that same frequency. Most electronic sibilance is of the second type (dropped mics can do this), but it sounds like what you are experiencing is of the first type. So it might aid you, and you have the ears for it, to listen closely to see if there is actual distortion there, or just an abrupt level change there.
Equalization is at best a workaround. It is best to fix the issue at the source. You would also need a 32-band EQ to be able to notch that frequency effectively (and you can't EQ actual distortion, only minimize it). a 12-band or less will distort the response too much for "golden ears". I own a 32, but good luck finding something that can be used in the digital domain or for 5.1. I don't think EQ is your anwer.
The other thing is the nature of digital audio. Once digitized, and assuming all parts are working properly, digital audio can't possibly become distorted without performing math on it; it is completely represented by binary coefficients, and they don't change unless we change them on purpose. Of course if you send digital audio where 0 dBFS is calibrated in the target system at one level into a destination system where it is calibrated at a different level (and that is technically a change in the math), distortion can occur.
But that does not seem to be the problem here either.
Sibilance or any other distortion in properly designed and working digital audio is rare, indeed; that is usually an analog issue (or issssssue, as you are unfortunately used to hearing it. Sorry, couldn't resist). But the critical thing there is "properly...working"; I suspect things are not working as they should, most likely in the DVR, and when things are not working properly, all bets are off and all of "what should be" regarding digital audio is completely out the window.
Audio arrives in your DVR (for HD sources) typically as AC3. It is then decompressed back to PCM for HDMI, I think, and DAC'ed for analog out. If the analog is good, that might point to the AC3 decoding in the DVR as the problem, or not. If both are bad, that points to either a problem in the DVR or the AVR (you could try the HDMI direct into a TV to eliminate the AVR), with that problem most likely close to the DAC or decoder (it may even be the same chip). That all has to work right for things to sound right, and there really isn't much more that could possibly go wrong.
So, the smart money here is on a defective HR24. There is a small possibility of simple idiosyncratic incompatibility between the DVR and AVR, but again, those would be the longer odds.
Were it me, and without more info, I would have the DVR exchanged.