I have both DSP and non-DSP versions of the One (as well as both versions of the Tanchjim Zero & Tanya). To me, the One are fine IEMs, and the DSP versions allow you to correct/adjust the FR to your liking, with your corrections “following” the IEM—a great concept for entry-level IEMs IMO.
Again, in my experience, the DSP version of the One has more than enough power to play louder than what I would ever stand.
The Tanchjim app (Android) is easier to use and has been more reliable in my experience than the Moondrop app (for Moondrop’s FreeDSP, CDSP, JIU, MAY) which often fails to detect the cable/IEM.
The Tanchjim App gives you some presets + a 5-band PEQ, but only of the peak-type filters (you can adjust the Freq., Gain, and Q-factor on each of the 5 filters). Whenever you save a setting (not when you fiddle with the filters), it resets the USB connection, so you need to re-allow exclusive access in Android.
I’m not sure if the iOS app would ever work due to Apple restrictions on USB communication—there are two interfaces exposed: a UAC-1 compliant (up to 24/96) and another one (type?) with 5x endpoints, one for each of the DSP filters.
The Tanchjim DSP-enabled IEMs are built around a KTMicro chip providing the USB bridge, DSP, DAC and HPA functions (I suspect it’s a KT0210, but it’s unverified).
One detail: if you change from cable-down to around the ears, you have to swap the L & R cables
so that they fit the IEM connector properly as you also swap the IEMs
EDIT: I haven’t checked if the DSP version plays DSD files (not that I care much…).