I see you're liking the TH900 a lot! I will be purchasing another one soon.
Don't forget that your unit is very special in that your earcup wires and cable are all extremely good. A well-burned-in silver cable does not sound "bright" as people always think. It results in a much fuller body, deeper more layered soundstage, more realism, and everything is clean and crisp, no blurring between the lines. The Q French Silk is quite the cable as well so what you're hearing might just be due to the infinitely better wiring that's inside the cables you're using than anyone else here since most have stock and it's made up of SPC (Silver plated copper) which tends to have some harshness in the highs.