Ryan,
Your description of the harshness you describe that parallels your volume level and your relating to fatigue when you really turn it up really points to your room as the culprit.
Those speakers a not at all harsh or grainy. They are more to the softer, laid back, and smooth side.
What you are hearing that you are not liking are the room reflections that are interfering with the primary signal. The sibilance you are hearing is also likely to be caused by a primary reflection or even a secondary reflection arriving so near in time to the non-reflected sound that it is perceived as the same. Good room treatment will smooth it all out and take care of those problems.
I would love to sell you the high quality Sonicaps, but if you have only a little to spend your money will go further with a well treated room than anything else.
Attack the primary reflection points and the wall behind the speakers first. This includes the corners of the room behind the speakers too.
Here is some really good, and cheap, DIY room treatments that you can build:
http://mywebpages.comcast.net/kidder...NEL/Panels.htm
After you get your room in order the Sonicaps will be a nice upgrade that you can appreciate.
I'll even through in all new heat shrink for free, and some more solder.
Plus, I know the guy pretty well that assembled your networks (me) and I know it will be pretty easy to de-solder the current caps and solder in the new Sonicaps.