I personally hear a difference, as the DX200 is brighter. Some prefer that, maybe some don't. Dobrescu has a ton of equipment history, so you may want to factor his opinion, maybe more so that mine lol.
The higher up the chain, I think the difference become more miniscule, as personal taste (and iem match) come into play.
The X7II is a big jump over the X5III, but I've read that some don't even hear that difference, so who knows lol. my point is, when dealing with music and art, it's subjective I guess.
What is your focus; treble, mid-range, user interface, tidal, dsd, USB out , etc...?
Have you considered the Hiby R6? I found the R6 and the X7MKII the better "sound" comparison. Am5 (X7II) has more power, but articulate detail was more pronounced across the board on the R6, imo. The speed is world's improved too.