Looking for a speaker cable with a relaxed sound.

Wireworld Eclipse 8 would fit that bill.

I would second this suggestion.  I have heard the Wire World "Eclipse" level XLR interconnects.  They have very excellent resolution, but they are just very slightly laid back (definitely not forward or bright).  I think the same would go for the "Eclipse" level speaker cable, which is pure copper.

I would NOT go to the "Silver Eclipse" level or above, which contains silver / silver clad conductors.

Purist Audio Design is another good recommendation for this.

Not answering your question, but I assume you've played with toe in and tilt to see if you can achieve a better balance?

This is the problem with speakers that aren't custom tuned to your ears.

Just kidding.  :)

Depending on your price range (and contradicting the posts above),
Wireworld Platinum Eclipse 7 speaker cables are the most relaxed, least bright cables I've ever heard and they're all silver. 
That model is at least 50% off of original prices, if not greater.

So you’ve all this detail and spent a bunch extracting it. Now you want to dull it back down a little? Try this experiment. Romex 14/2. The white one from Lowes/Depot. Use only the black and white wires.

Depends on your budget...there are some good choices
I would try ’Sorvelis’...their entry setup....talking about relaxed...Schubert sonatas went from relaxed to ultra relaxed on my floor standers by BMC