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

"A cable is a source of potential trouble connecting two other sources of potential trouble"

Wilson’s generally like Transparent. As mentioned, it is what is used internally. I’m not sure how much it matters which ones particularly. Might be worth a call to either company. Power is definitely a consideration, I’ve kicked up my power lines with Cardas power and replaced my primary outlet and use Furman conditioning. I was VERY surprised at that change of these “tweaks”. I didn’t buy it at first, but power can make all the difference in low end delivery. Just more juice... another is placement. Have you played with that much? Moving them, even a little, can make a pretty remarkable difference.

Impressions from the OP:

1. The Transparent Audio RSC8 reference speaker cable does sound good with the ARC tube amplifier ---> the Wilson Sasha speakers combination. This realization came after several days of listening;
2. The Wilson speakers seem to love vocals, especially opera, and the more recent crooning from Diana Krall and similar artists that audio dealers love to use in demonstrations. I don't like opera or the Diana Krall, Norah Jones and/or Frank Sinatra genre all that much - I much prefer the Beth Hart (and old Joni Mitchell) genre of female vocalists, string-based classical music, orchestral music, hardcore improvisational jazz including bop, bebop, and fusion, and rock;
3. I realize that I eventually should get rid of my tube power amplifier and get a powerful solid-state amplifier, but then these Transparent Hi-Z speaker cables may not be a good fit...jeez!

I would like to thank everyone for their great feedback...I am still searching...The grateful OP (as in "Long, Strange, Trip")

Leaded solder is even softer than lead-free, so it flows even more. With speaker wire, it just means your screw contact will loosen up and your contact resistance goes up. The average power is normally low, so no biggie. When people do this with AC wires, it can lead to arcing and fires.