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

If those expensive wires are causing your amp to be unstable, then the low cost copper wires will be better. You may be confusing "detail" for artificial high frequencies.  Most claims about high end wires is marketing, but highly capacitive wires can make amplifiers unstable.


If it is bass de-emphasis, that is harder to address without an amplifier change or tone controls.


Sounds like your room is well designed, but a wide dispersion speaker can seem bright where a narrow one does not. Frequency response is on axis but we hear room response.


The amp instability can be measured in minutes with an oscilloscope and a signal generator. The bass de-emphasis can be detected by swapping out for a good high current amp, and a room response issue with a measurement microphone and something like REW. Not sure who you know who can help, but may be a better path than buy and try with unpredictable results.

Ruraltrauma-    I might have missed it but I still don't see where you told us the speaker cables you tried that you thought sounded OK.   That is kind of important.   If you tried a brand that does not have the brightness in your system you should consider moving up their line.   Many manufacturers try and voice their cables with the same "house sound". 

I am open to suggestions...

@ruraltraumasurgeon When you say "open to suggestions," which areas specifically? (Beyond your original post regarding speaker cables)

When cables are in the wrong direction 🔜 guess what? They sound....wait for it....bright! Hel-loo!

Folks-

I use twisted copper cables without terminators. The system sounds better, so that's where I may end up (at the beginning, pointed in the right direction).

I am borrowing some hi Z (high pass roll-off?) Transparent reference cables to try out today.

Thanks...