I didn't hear the DT770, but i had the DT1770 for a while. Again, treble was a bit sharp, smaller soundstage, it was a bass canon, not very resolving. Again, on a tube amp i could enjoy it for "wonky big bass fun". It had the best passive isolation of any closed backs ever though (i would say now that the Maxwell is on par).
Of course you can use EQ, i'm not a fan, but sometimes it helps, but often times you can only roughly EQ what bothers you, not precisely. The Maxwell will be better, it's perfectly tuned because it's already using EQ internally. It will also be more detailed and more clear sounding.
Dynamics are basically how much air the driver can push and make the sound feel more impactful (punch & slam, physicality). Examples:
The Unseen - End Of Green at 0:42 when the drum kicks in.
Celeste B-Sides - Old Site at the start.
Supermassive Black Hole at the very start. The example that i tested when i could not listen to my own music was
Queen - We Will Rock You, that song was basically on every listening device at Highend Munich. When i listened to it with Stax or the DCA Stealth it sounded so flat and dead, as a listener you had no intention standing up and rocking with the song.
Normally dynamic drivers (such as the Beyers) have better dynamics than planars (such as the Maxwell). You cannot EQ dynamics (you can bump up the upper bass for example, but it won't have the same effect, dynamics are not the same as volume). Even some very expensive headphones often lack dynamics (Dan Clark Audio, Meze...). Focal headphones for example do have very good dynamics. When you heard a highend headphone that does dynamics exceptionally well (the Abyss 1266 TC is the #1) your mind gets basically blown by how much dynamic songs can sound. Often times dynamics are also very dependant on the amplifier, the Hifiman Susvara needs very highend amps and it will sound very dynamic once you spent (too much) cash, up to the point where you hear (feel) the air moving from not only drum impacts but also the string playing of guitars. Of course the recording quality needs to be exceptional for that too, like
The Pineapple Thief - No Man's Land. Some reviewers talk about micro- and macrodynamics.
So, TLDR: Get the Maxwell, you won't be disappointed. And then later get a tube amp for the DT1990 and A/B them
.