Congrats

, I've never tried usb dac feature :rolleyes:
My personal opinion after modding:
- sound is more airy, less congested, soundstage is wider.
- sound is more refined, notes have more weight, bass is deeper, detailed, not boomy, male and female vocals are slightly better, treble is more detailed with good extensions
- impression of more power on HO and LO
- gain doesn't change sound signature anymore (mid-gain V shape, high-gain warm), more precisely it's almost not noticeable. Before that I could'nt use mid gain, now it's always on.
Some updated impressions with 2.5.1 L0, on some tracks, female vocals can still sound harsh on S words but less than on 2.4.0 L1.
I retried quickly other firmwares with ultimate cleanup on my modded DX90:
- 2.1.5 L4: analytical, bright sound, very good highs
- 2.4.0 L1: balanced sound but slightly warm on bass and lower midrange
- 2.5.1 L0: most balanced sound, according to Ibasso, they updated WAV, FLAC, DSD decoding engine. Sound is more neutral and seems to have more resolution and transparency, soundstage has more height/depth now, which is very good.
Depending on personal preference and synergy with gear, one of these firmwares would suit your taste. That's why it is preferable to try it yourself. I just can say what I hear.
I prefer using 2.5.0 L0 pairing with slighty warm headphones
Btw, I didn't like stock 2.5.1.. rather flat, veiled and not very good extensions. :blink: Maybe it's just me.