Had LCD-5 before, and have chance to try MM-500 today, side by side with LCD-5 and Abyss Diana (Phi and TC).
In short: Definitely a sublime headphone for the price!
In reminds me a lot of LCD-5, but, this is a big "but", MM-500 is like LCD-5 with proper EQ already installed.
Too much midrange of LCD-5 is gone now, and instead, there is more airy feeling on treble area, combine with a little more punch and heft at bass area. Listen to MM-500 is like listening to nice near field studio monitor speaker. Highly accurate decay and transient, no big boom bass, no harsh sharp treble, just a transparent and fluid transient.
LCD-5 may still hold the flagship status as produce more micro detail, wider and better height in soundstage (about same depth). However, lack of treble air, and too much midrange quantity in LCD-5 become deal breaker to me. I sold LCD-5 already, and never expected to like the new tuning of Audeze. MM-500 may change my mind!
I can imagine, if only MM-500 came first to the market, LCD-5's sales (with price more expensive about $2800) may take really big hit. MM-500 definitely much closer in performance than $2800 gap.
p.s: Abyss Diana TC and Phi may have better clarity and detail with bigger soundstage, but they seem colder and thinner sounding at midrange area, and "too analytic" for lesser than great recording quality, make MM-500 more versatile headphone overall.
Tested with Chord TT2