Help me tame the brightness of my Triangles

I bought a pair of Triangle Zerius speakers a month ago, and in some ways they're the most amazing speakers I've listened to. Incredibly open, detailed, fast, and dynamic (as advertised).

But I also find them to be too bright and too hard for my ears, at least with a good amount of my music. I've taken care of the obvious things, like break-in (approaching 300 hours now) and matching with a warm system (Rega planet 2000 cd player, Unison Research Unico integrated amp with Mullard cv4003 tubes). I put little thought into cables .. i'm currently using straight wire rhapsody 2 interconnects and 20 feet of audioquest gr8 speaker cables.

The hardness comes in the upper midrange/lower trebble, typically at high or moderately high volumes, and typically on vocals and guitars. Especially if the recording is at all aggressive. The brightness is just an overall sense of the tonal balance. It seems lighter weight than what I hear in live music. I expect the music to have more weight and roundness (this is why I have the Planet and the Unico to begin with).

I've played with position and toeing in. My room is large (about 16 x26 feet with 10 to 11 foot ceilings). It's slightly bright and splashy, although i believe most of what I'm hearing is the direct sound of the speakers (the tonal balance is the same when I get real close).

I'm wondering about new interconnects .. perhaps cardas. the Quadlinks seem like they'd make the most sense. Any thoughts on this? How big a difference they might make? Would the Cardas Cross cables be unreasonably pricey in this system?

I'm also wondering about tubes. The Unico with the mullards has a wonderful, liquidy midrange, and great transients and dynamics. Are there any tubes that might darken the sound and soften the lower trebble without killing detail, dynamics, transients, and soundstaging?

I suspect most people would find my system sounds more balanced than I do ... my ears seem to be pretty sensitive to brightness and hardness. But it still seems strange that these speakers that everyone seems to like can sound bright even with these other componens I've chosen.

Thank you for any thoughts you might have.