speaker cable that will soften the highs

Cardas "Cross" line, such as Cardas Golden Cross.
Art

You have to ask yourself what would cause a cable to do that -- then, if you are satisfied that it is possible and the reason can be ascertained -- look for a cable with those attributes.

Or, if you want to soften the highs because the highs are "hard" -- you might look into your room. I'd be willing to bet your room is causing the hardness in the highs and trying to treat this problem with cables will send you on an expensive merry-go-round.

Rather than trying to find a cable that will roll off the high end, I would hire an acoustical consultant for a few hours to analyze your room and suggest treatments.

Cardas Cross, Jena Labs, MIT

Resbeck's suggestions re room acoustics is a good one. A lot of brightness stems from 1st reflection points on walls, ceilings, and floors, as well as the amount of toe in used. Before you start spending money on cables make sure you have your set up down. If you want help, describe your room dimensions, openings, furnishings, speakers, present set up (location of speakers and listening position). Don't know that you need to hire a consultant yet though.