Recommendation for an audiophile speaker cord that is not "bright"?

Hmm.  I believe Nordost has the rep of tending to be forward or bright.  Silver plated conductors, of that which Nordost leans heavily, can be "bright".  I'd suggest cables that do not have silver content, such as Wireworld Eclipse 8.  They are a 9 gauge cable, however, but with speakers like the Sashas you probably have a pretty stout amp.

Staying in the solid copper conductor design, Audioquest also makes some great options, but frankly they get pretty expensive.   

Give Wilson a call and see what they recommend. They do a lot of shows every year, not sure who they partner with. Off the top of my head I would try Acoustic Zen Hologram, Kubala  Sosna and Kimber cable.

If you like the cables in general but find the brightness an issue, you might try different plugs.  The top of line IEGO 8095 is rhodium over silver and this plug has had a smoothing effect in my system.  My speakers use Eton metal dome mids/tweeters and can have more bite than I like.  My power cords are DIY solid core copper with silver plate.  I usually use Oyaide 004 plugs but have added the IEGO's to a couple cords and the detail is still there and the highs are at least as open and transparent but somehow smoother without the bite.  Something to consider.

Anticables, really tough to beat
then if ya want to spend a bit more money an Audioquest with DBS, stock to copper

have fun, enjoy the music and the search 

Cardas are known for warm sound, except the "Clear" model.