Cables to settle brightness

Do you have optical ethernet isolation to your DAC? If not I would definitely look into that. It removed a fatiguing bright scrim that I suffered with for years. I have a Sonore optcalRendu going to an ultraDigital to I2S on my PS Audio Directstream, and I replaced all the switch mode power supplies with linear,

I'm willing to bet that it isn't your cables or your DAC. It is noise. And it isn't really bright as much as it is brittle, like fingernails on a chalkboard in the middle of the high end. You don't hear it specifically until it isn't there and you go back to your prior configuration. It'll be either power-line noise or source/transmission noise coming through your router or switch (or both). In my experience, filtering or fixing one or both will provide noticeable results.

@bondmanp I second how do you know its not the DAC? What was your original Digital chain you mention?  I use Sonore along with many others and have zero issues with treble. I have Be tweeters in my Sorpras. So if it was going to be bright they would show it.

for the OP I agree do not use Silver. Tried my Ver1 Nordost Blue Heavens and I hated them with these speakers. Cardas now and I love them. I have the PowerPlant 20 with everything plugged into it.as well. No harshness at all. Stay copper. I use Audioquest Mckenzie for interconnects.

@earthtones I am considering the Sonore optical converter boxes.  Reasonably priced, and returnable if it doesn't do the trick.  My digital chain is already kind of a Rube Goldberg contraption, and this would make it moreso.  But if it works, who cares?  As soon as I have the budget for it, I will try it and report back.

@fittebd my old DAC was a highly modified Beresford, maxed out at 96/24 and lacked USB.  I still have it, so if I had some time, I could go from the UltraDigital to the Beresford with a coax cable.  I have enough inputs on my pre to hook both DACs up at once.  I would need a pair of decent ICs, though.  I know I really should do this, as it would tell me if it's the DAC or all the other stuff preceding it.  Yes, I have an inexpensive network switch, and no, I have not upgraded its power supply.