We got pretty excited about the new generation of HiFiMAN planar magnetics when we first tested the
HE-1000, and since the Edition X shares a lot of its technical features for less, expectations were admittedly very high. I took the Edition X through my got-to songs after burning it in for 100 hours, and it did not fail to impress. To start off with, its efficiency is noticeably higher than with the HE-1000. The 13 dB/mW increase means that you get the same volume at roughly two-thirds the power.
Despite missing out on all the fancy materials that went into the HE-1000, the Edition X does produce a result that is no less thrilling for a bit over half the price of its elder brother.
The Edition X gives you the same kind of fidelity in the midrange, albeit with a slightly smaller sound stage and a somewhat more neutral tonality. The slight shift in tonality toward the neutral side might be preferable over the generally more musical HE-1000 to some, and it saves you $1200. The sound stage is much more intimate and more in-line with what you get from an upgraded set of HiFiMAN HE-560s than what you get from the HE-1000. It is perhaps only so in relative terms between the Edition X and HE-560 because the Edition X maintains separations better in complex passages.
The midrange is best described as drier, and it definitely brings out more nasal noises than the HE-1000. The Edition X does seem to have an even faster decay, which makes why it does not exhibit an even better sound stage than the HE-1000 a bit of a conundrum, as I am used to the thought that good transient response would make it easier to pick up on spacial audio clues.
Playing around with different amplifications reveals the Edition X to be less picky when it comes to amplifiers. Going from the C5D from JDSLabs to the Schiit Mojlnir did not lead to a hefty upgrade in sound quality as expected. The HE-1000 is also pretty easy to drive despite its much tougher numbers, but a swap from the C5D for the Schiit Mjolnir led to larger improvements.