I agree with the nasality comment on the A900x, but that's the only real chink in their armour, well that and the bass is a little overblown at times, but fun and very tuneful). Noticing that my Sonys had some small holes factory bored in the back of the earpiece to make them very slightly open-backed I wondered if modding my A900x in a similar way would help eliminate that nasal, choked quality that seems to be encumbering them a bit. I tried to add a photo of my Sony's drilled earpiece but message says I don't have permissions to (maybe because this is my first post). If that facility comes later I'll add the photo as some may find the concept interesting - DIY semi-open cans mod.
I went on a mission a few weeks ago to upgrade my 20+ year old Sony MDR-CD550s, thinking a couple hundred $£ should get me something to blow them out of the water in all respects, but the journey hasn't been so simple. I bought HiFiMan HE-500s (great bass slam but not very tuneful bass, and voices and timbre of acoustic instruments is suprisingly veiled leaving an overall congested or veiled sound, not the airy freedom I want), Shure SRH840 (nicely balanced but slightly bass light, and overall a little dry for my tastes, though they're one of the few that are good with no EQ: I intended to listen through my main system of Naim CD player and Lehmann Black Cube Linear HPA so no EQ available in that system), a pair of DT880 Premium bought on eBay that haven't quite reached me, so I can't comment there just yet, but will update this if anyone's interested afer they arrive. Starting with the notion that the HD650s may be the ones, then altering my opinion o favour the 600s, then stumbling upon the we;ll reviewed HE-500s that threw me off track, I'm slowly coming back to thinking that the HD650s might be the best fit for me and my budget after all, so it's encouraging to hear someone say they're ultimately better than the A900x, that I'm 85% content with. Don't know if I'll ever find the perfect headphone - has anyone else done so?