I have never heard of anyone finding the treble to be harsh on the Nightowl. This is one of the least fatiguing headphones you can get in regards to the treble response. It was designed to have an extremely smooth upper frequency response. I have not heard the FiiO Q5. Perhaps it just does not pair well with the Nightowl. I have a Creative ZXR sound card which has all the opamps upgraded to the Burson Audio V6 Vivid opamps. I use this as my DAC. Connected to that, I have the Audio-GD C-2 (2017 Edition) headphone amp. This is an awesome sounding setup, and I have never heard any harshness or fatiguing elements in the treble on my Nightowl or Amiron Home.