I've reduced brightness several ways: transport, power cord, cables & interconnects, power conditioning, tubes, toe-in and sound absorbing gear.
I had very good improvements going to a tube preamp.
I had amazing, jaw dropping improvements by changing a transport.
I heard night and day difference between interconnects. IMHO, if neutral cables were easy everybody would have them. I find cables to make a tremendous difference. Try borrowing some cables/wires and see if it makes a difference. If so, go to audioadvisor.com and look at their discounted audioquest or kimble kable gear (not that this is better than Cardas or other wire). I've frequently heard Cardas can tame a bright system but don't have experience with them. Anyway, if the cables are the problem, then it's an easy inexpensive solution. I'm suspicious about your wire and cables.
On the other hand, some gear is made bright (like my previous Adcom or Micromega gear). Try switching out components with friends and see if you can find the culprit.
Recently I found a stock power cord to have a larger impact on sound than two different expensive DAC/filter combos. This in comparison to an inexpensive DIY power cord design by Crump. Two of us were comparing gear and felt one set was brighter than the other, until we swapped cords, and suddenly it was the opposite.
Less or zero toe-in should sound less bright at the sweet spot, but worse in the rest of the room.
Sound absorbtion at the first reflection point on the side walls can help a lot. Also, add carpet and wall hangings if you're in a bare-walled sheetrocked room with wood floors.
Good luck.