It is just slightly bright, I'd say airy, but not sibilant at all. This is a wrong term. Being sibilant is when a headphone emphasizes certain high frequencies with high amount of graininess and lack of detail. Arya is a total opposite. It is one of the most detailed and revealing headphones. There are just slight bumps at 3-4K and 6.5-8.5K. So the term 'sibilant' is absolutely irrelevant. It is bright but in no way sibilant. Try lowering these areas in your EQ if you hear them as too bright. I never EQ my Arya because I bought it exactly for the purpose of hearing everything with the most detail possible while preserving natural tonality of the sound. I'd rather refer to Ananda for a more laid back sound. Slightly less detailed, more natural tonality, not so bright, and twice cheaper. If you don't need a precision tool for mastering like I do and you are treble sensitive then Ananda is a better choice.
The Arya's bumps in the high mid and treble areas can be tamed with EQ while there are headphones like Focal where the inherent metallic timbre just can't be cured due to the combing distribution of peaks and the material of the membrane which emphasizes the whole timbre rather than separate frequencies. Trying to battle those peaks will deprive the Focal headphones of their ability to resolve detail because their peaks seem to be interdependent.
In regards to ZMF Auteur, it is too gooey for me but I'd say there is more traditional representation of decay due to the dynamic nature of the drivers. I still like the immediacy of planar drivers more. ZMF Verite would be a much better alternative to the Arya than the Auteur. Crinacle rightly places the Arya much higher than the Auteur both in terms of tonality (A+ vs A) and especially technical performance (S- vs B+).
