I do like the ZO2.3 I have and actually use it for bass boost more than I use E11 as amp. The problem is it hisses with some of my low impedance, high sensitivity IEM so I can't use all of them with ZO2.3. As an amp, it isn't the best around; but as a bass booster, it is great. That's why I only recommend ZO2.3 for those who want a bass boost first and an amp second.
Haven't heard the D7, and likely won't as I have little use for another USB DAC for now. When it comes to iBasso, my attention is on their ultra-portable amps.
Do note, capable of driving a headphone and driving it well are two different things, especially if you put synergy into the mix.