I think this thread might also interest you, because it deals with many of the same questions you’re grappling with here. Even if you do not intend to use EQ, it still addresses the question of whether a good lower end headphone can sound as good as a good high end headphone. I’m still a bit doubtful about this for a variety of reasons. But it’s an interesting question.
Also, when I say there are sonic differences between different kinds of drivers, I attribute a good bit of that to differences in distortion and impedance. If you compare the frequency response of open passive dynamic and planar magnetic headphones though, there are also some interesting differences between them.
This site conveniently has 5128 graphs of both the HD600 and Arya Organic, so you can do a direct comparison of their FR. And the differences between them are somewhat indicative of differences you’ll often see between open dynamic and open planar headphones…
There are other open dynamic and planar headphones in the Earphones Archive graphing tool as well, if you want a more fullsome idea of the differences. And you can change the color of the “squigs” so that all the dynamics are red and all the planars are blue to more easily compare them and see the differences.
You add more squigs to the graph by pressing the plus sign (+) after the name of the headphone on the list. The colors of the squigs are changed with the colored dots to left of the headphones names below the graph. That dot brings up a color wheel so you can make each squig whatever color you like. I’d post a screenshot illustrating this, but I’m not sure what the policies are here and on Squiglink for somethin like this. There is also a dark mode for the Earphones Archive interface if you scroll the toolbar above the graph all the way to the right.
The planars tend to extend deeper into the bass and sub-bass. They also tend to be more withdrawn in the upper mids around 1.5 to 2 kHz. And they tend to have more “air” in the highest frequencies.
Not all dynamics and planars follow these rules. But generally speaking those are some of the more common differences you will see on many of the better and more “neutral” open/passive models of these headphones.
Listener also has a graphing tool where you can do similar comparisons…
I wish there was a Squiglink tool for all the 5128 measurements on Headphones.com as well, with HBK’s stock 1/3-octave DF compensation curve.