Well, after some extended listening, I've decided to return the X-10. It definitely improved the "digital glare" on some recordings, but muddied up the bass (some midrange too) on everything else. For MY system, the downside was worse than the benefit.
I've decided to keep my components as is, and upgrade my speakers next. As much as I'd love to get the ML Summits, I can't justify the expense, so I plan to get the ML Vantages, which go down to 34 Hz (rather than 24 Hz of the Summits). From what I've heard, and read, these latest ML designs are their best yet, and the new stat panels have more radiating area and are less "bright" than the older designs.
If I still end up with listening fatigue, I'll probably upgrade to a tube pre-amp (probably the Modwright).