recommendation for speaker wire to soften the highs if possible

@nasaman  I can start a dissertation on how to use LTSpice to run simulation on how an LC filter strapped in parallel to an LCR load (speaker) will work to roll off high frequencies at which point by how much of a slope, or I can just suggest with about $10 investment you can get some caps from parts express and a few pairs of resistors, one can try them out for a binary search to get where one wants in terms of taming the harshness of the tweeter.  The simplified guide is:  The higher the value of the cap the earlier it will roll off, the lower the value of the resistor the steeper the roll off curve is.  I know it is never as satisfying or confidence-building as spending thousands on cotton wrapped oil impregnated cables with a mystery box, but it does save some time.  https://www.electrocube.com/resistor-capacitor-networks

I reccomend Cardas,they do a great job of warming up a system and subtly rolling of highs. I dont recommend them for tube equipment though.

I certainly agree about Cardas, I tried that for my DAC before switching over to the isolation transformer. It was an improvement, but it was a bandaid not a fix.

You might try a overpriced  power conditioner that helped for me