That's a bit too much of a generalization in my opinion. The older 9018 Sabre chipsets did suffer from this treble issue caused by the overs not being properly taken care of by the rest of the circuitry. Not so much Sabre's problem, but rather the DAC designer's issue. There were some very well implemented 9018 chipsets. Thankfully the newer 9028/9038 generations take care of this within the DAC chip itself and has made the DAC designer's job easier in this regard.
You've made some excellent recommendations on DACs and I pretty much agree with all of them.

That's the thing with such a revealing amplifier as the GS-X Mk2, it will let you hear your DAC like no other amplifier I've come across. I would recommend a DAC with balanced outputs as the GS-X Mk2 is a fully balanced amplifier and requires both balanced inputs and outputs to run balanced and allow you to access all of the power of the amplifier. I might add the Benchmark DAC3 HGC and Chord Hugo TT into the mix as it was also quite excellent. I'm currently using the Chord DAVE and when I need some extra juice for say the LCD-4 or Abyss-Phi headphones, the GS-X MK2/DAVE combo is quite spectacular!