Cables to settle brightness

OP…

@vonhelmholtz nailed it. 
Forget cables for now. The internal mcintosh dac is your issue. It’s digital/harsh sounding. Cables won’t cure that.
Get a good DAC. Worry about cables later. Stay $5k and up MSRP for the DAC used or new. There are multiple threads covering this topic under digital (latest discussion should show up at the top).

Also, I’d keep the amps plugged into wall. 

I should add that the DAC that I criticized was the DAC2 inside my MA12000. I think this DAC competes in the $1000-$1500 stand alone DAC range, but we each have our preferences/bias for what we consider musical. You might want to chat with Juan (blisshifi) in that I believe that he shares this bias and he helped to get my system where I wanted it.

If vinyl doesn't have the problem, it is in your dac.  Some DACs have a voltage setting. Turning down the voltage can reduce harshness.

I keep saying that cables aren't tuners and many disagree.  But you're spending a lot of money swapping out the wrong component.

Jerry

+1 on upgrading the DAC.  Your amp, preamp and speakers ae al in the 'not bright at all' category (to me). 

Many will recommend the dac and or streamer /dac they have.  Plenty of smoother DACs out there, and you have expensive gear.  Demo some!  And yes, most find all copper smoother than silver or silver blends for interconnects, power cables and speaker wires.