silvermuse
New Head-Fier
If you're in Seattle, I'd check out Definitive Audio and maybe the Best Buy in Northgate. Definitive Audio has some flagships you can demo like the HD800S and Focal and Best Buy usually has Sennheisers up for demoing.
I agree about the JM XTC Open, imo exploring boutique options is something best done when you have a better handle of what you want in a headphone.
Thankfully, I literally live around the corner from Definitive Audio, less than 2 blocks. Unfortunately, I had the impression that they just did appointment-based home theater sales, but it looks like they have headphone demos. Absolutely checking them out this week and will learn a lot.
660S2 definitely seems like the option, just more expensive than other 6-series. I've seen it as low as $300 and I think I'll get one for that.
I'm going to pass on the 800S for now, but I'd grab an Arya if another one shows up for like $600.
Otherwise, I definitely may look for a focal Elex just to see the build quality and get something that ought to complimen the Hifimans, at least I've heard?