Barnstorming review yet again, Alex. Your reviews have become the porta-fi wiki of Head-Fi, which is really cool. Helps when you know how to comprehensibly describe exactly what it is you're hearing.
I think we (Nio users) have been waiting for quite some time to read what you made of it, and your impressions seem to tally very closely with mine. I've been using the terms organic, smooth, natural and laid-back to describe the Nio from the very earliest days, and was pleasantly surprised (and relieved that I'm not deaf!) to read them back in your review.
I personally prefer the elevated bass and slightly more euphonic vocals with the M15 over the N0 (which I bought to experiment with), but I may just go back to N0 to hear again how it opens up the upper registers. I haven't even bothered plugging the MX in because 'mid-forward bass-light' is my audio kryptonite.
One thing I did notice is how you were looking for (and not finding) too many similarities between the N8 and Nio, and that's because Nio isn't similar to the N8...it's similar to the N8 Uni (which, I know, is not a commercially available IEM). Just one look at Crin's graphs pretty much explains it.
Thanks again for this review, much appreciated.
PS. Did you get to hear the Nio with the PW 5 or PW 10 cables? I'm loving it with the 10 (8-wire) and have a 5 (8-wire) on order, both of which I'll cover in my own Nio review.
Edit: Alex one more question if I may - is there any hissing with the Nio on the balanced out of the R8 (with/without turbo)? There's absolutely none on the R6 Pro in high-gain balanced mode so I'm curious if the R8 is actually noisier than the R6 Pro.