Try the DT880s (but seriously, just get the 250 ohm, atleast), it is tuned much more neutrally than most Beyers, and unlike Amiron is available in a ruler flat phased, 600 ohms (and for under $150!). The HD800s, that Senn would release ~20 years later at close to 10x the price has a remarkably similar tuning.
If you spend some time with a range of Beyers, I imagine that you would hear what the objective measurements (and underlying electrical theory) show: higher impedance improves damping which Beyers generally benefit from. This ties in part to what you call 'loudness' (although in the DT770's case particularly, it has enclosure resonances as well).
I am glad we see eye to eye on my dislike on this design. I generally found MD does (did?) a very great job at curation and this strikes me as a nasty misstep.
More fundamentally: part of Beyer's core identity is a high impedance dynamic. . . I'm not aware of any other 600 ohm voice coils (?), certainly not in this price range. Their 600 ohms have phase uniformity like a planar, they really meet Dr. Beyer's original vision of a dynamic that competes with an electrostat. This drop is like spending years on an exclusive collaboration with Ferrari that turns out to be a scooter (Introducing the Ferrari F5x Go!)