These are measurements of the MD+ (RED) overlapping the ER4XR: And this is the old FR for the MD+ before it went through retuning: I feel like the IO matches this FR quite closely except their peak in the upper highs is situated closer to 7-8k hz and that dip isn't as large, similar to what I hear from the Lyra II. I don't find them to be slightly V-shaped at all, personally. They sound pretty forward throughout the mids IMO and I'm willing to bet have a similar rise in the 1.5-3k hz region. I normally use the vocals by Kelvin Swaby from The Heavy as my sibilance test as his 'S' and occasionally 'T' sounds are usually triggers. Try the track "The Apology" to get an idea of what I'm talking about. It still isn't bad enough to really bother me, but it is present to those that may be more sensitive to it than I. Otherwise, I pretty much agree with everything else you stated as well.