Cables to settle brightness

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.

The Sonore will mask much of the noise generated by a generic network switch.  That is what it was designed to do.  My guess if is its really that new to you, new sound is different and takes time to adjust.  You could try just putting the old DAC back and see what happens.  not the best A/B, but you can tell if the harshness goes.  Then try different interconnects and see if that helps with new DAC