I understand EQing to user preference, but to fix a considerable problem I'm not sure. I have seen a few mention that they have found EQ settings that have improved sibilance, but there does not seem to be a silver bullet for those who are reporting it. I have no experience with Foobar or other equalization software. I'm under the assumption that they actually assuming control of the computer's audio properties, so is it correct that I could use with MOG and youtube?
I have personally given up on Foobar as of a few days ago. I had some contention using it with the Wasapi driver as I was switching DACs in an out. I've moved over to Winamp, and as a preference, I'm happier, and my issues have gone away.
I basically drop the 6 KHz frequency down a bit and problems are solved. I don't feel that the EQ masks anything, it just controls the response, so that frequency is "tamed." You can control the amount of reduction that you want. Usually, just a few dB does it. Plus, when reducing that frequency down, it only eliminated the sibilants for me, but doesn't remove any of the other sound qualities that I enjoy.