I was fortunate to have Rn6 & Xe6 with me for a few weeks along the Australian tour, and these are pretty much the things I was most interested to compare and understand myself, so thanks for prompting me to share this sooner than later!
So, Xe6 vs Rn6. Firstly, both of these are amazing IEMs, and as you can see I've already made the full commitment to the Xe6. My listening with all 3 was with the silver ATOM module, as I find it gets the most of the kinetic bass performance without becoming too suffocating. I would only use gold out and about in a louder environment where isolation is important. The very obvious difference here is in the mid bass and lower midrange. Xe6 is significantly elevated here, which gives it an incredible warmth and casts an intoxicating glow around the music that I find highly addicting. Xe6 stage feels a bit more compressed to the middle because of this, giving it a cozy intimacy that fills my head perfectly. Rn6 by comparison is much, much leaner, hewing to a more 'correct' type of tuning in this region. This makes Rn6, especially with the red or black modules much more spacious, especially in stage width. So it definitely feels larger.... but for me it feels somewhat hollow when compared to the Xe6. I guess the best way I can describe it is that with Rn6 I feel like I'm looking at the music, whereas with Xe6 I'm completely immersed in it.
A track like Sofia Kourtesis' "Funkhaus" bears this out:
With Rn6 the sub-bass synths are very deep and satisfying, but pushed out to the edges of the stage. Xe6 takes those synths and fills them all the way into the centre of the sound image in a way that makes this track totally dominate my mind and, I believe, fully experience it. Now, Rn6 does have a few of its own advantages, notably details in the upper midrange and treble are much more prominent and easier to make out. Xe6 still gives you all the same detail, you just have to listen in a little closer to tease it out.
I was also very interested to a/b the universal Xe6 vs my custom, and for this I did use the stock cable on both to take that variable out of the equation. Of course, these are probably 90% the same as each other, but that last 10% or so is pretty important I believe. With the custom you get much better isolation, a perfect fit, and the kind of long-term comfort that you can listen for hours on end with zero fatigue. Another lifestyle difference with the custom is that the ATOM modules are much easier to deal with. But the biggest difference I heard was that the CIEM is much more
coherent than the universal. This is probably down to the difference in fit between them, and the perfect seal that you get with the custom. I had never thought coherence was an "issue" with the universal Xe6, but going back and forth it was more obvious which notes were being produced with the kinetic bass driver down low vs the BAs/estat up high on the universal; whereas with the CIEM the entire frequency response curve felt much more seamless and presented together as a complete whole.
So back to your specific questions
@paul_uk_81. I owned Z1R for a year or so, and I would say that if you want to double-down on that kind of tuning, then Rn6 would be the way to go. Or, if you want your bass done differently, then go for the Xe6, as it would be a nice complement to the Z1R. And if you have an inkling that you're going to be in for the long haul either way, CIEM is a no-brainer imho.