I updated the firmware 3 days ago and it sounded much better than before. The tonal balance is much better from top to bottom. The bass used to be a little heavy comparing to my other dacs, Chord TT2 and Merason Frerot (BB chip based). I am very happy with the new firmware upgrade. The detail and sound stage have also improved noticeably.
As far as the synthetic, glassy sound in the highs, I do not experience that. It is maybe due to the warm sounding of my tube preamp, tube power amp, and speakers.
My front end: LHY SW-8 -> Lumin U2 mini (via Roon) -> Titan Helen (via Wireworld Platinum Coaxial) -> Pontus II (via Wireworld Platinum I2S)