DIY Audio Heaven has published a review of the Edition XX. Key takeaway for me is that Franz generally likes it, but out-of-the-box it is not a headphone for the treble-sensitive. It has a similar 8 KHz peak to the one that I didn’t like in the HE-400i and a resonance at 6 KHz. Thankfully he provides a schematic for a passive inline filter to deal with the 8 KHz peak, for the DIY-minded amongst us
The other thing that gives me pause is the combination of low impedance and low efficiency. If you’re dealing with a current limited source, that seems like it could become problematic.