I've heard both the R70x and Ether on my home setup (not at the same time, but some weeks apart from each other), but the amp I used, the Garage1217 Project Polaris, was pretty obviously far from ideal for either of them. While I did hear the R70x much better amped by the Project Ember (with a 6SN7 tube), I can't say the same for the Ether, as I have yet to properly hear it from an amp that can drive it effectively.
I consider both headphones to be somewhat close to "neutral" and along the same sonic lines of the discontinued Grado HP1000—integrated, cohesive imaging with a strong mid-range (though the R70x may have more fullness & body throughout, along with quite a bit more mid-bass, while I suspect the Ether may be just a marginally bit thinner-sounding) with somewhat rolled-off low bass and high treble. Also, both the R70x and Ether lacked roughly the same amount of clarity to my ears (though probably the R70x was a bit worse, in retrospect).
I definitely think a formal direct comparison between the R70x and Ether would be pretty interesting. And I'd recommend a strong amp for such a comparison btw, since the R70x really needs a powerful amp and the Ether does as well. Something along the lines of either the Schiit Lyr or Project Ember (with a high-gain tube) at minimum.