You got it.
The Quads have deeper sub-bass extension, better bass detail/texture, and sound overall warmer than the Elex (but this has more to do with the mids and treble). The Elex wins on bass impact, but the Quads do an excellent job for a planar. By comparison, the Elex sounds a bit woolly and a bit boomy, but that's really only in comparison. The Elex does have pretty crisp and well-extended bass for a dynamic driver at that price-point.
Both headphones have very detailed and well separated mids, but the Quads pull ahead here. The Elex has a more natural tone, by which I mean a more linear mids section and one that balances better with the treble and bass. The Quads, I find, have a dip around 2.5khz that can make the mids and especially the vocals sound somewhat muted and occasionally muffled. Most of the time I EQ in about 4db there to give back some vibrancy. The Elex just has that vibrancy already, though occasionally it comes off as a bit aggressive sounding with, to my ears, a bit of a rise around that same 2-2.5khz area. In addition, the upper mids can show some glare on the Elex, causing things like electric guitars to blend together and sound strident or biting at times, especially in busier tracks. The Quads are less aggressively tuned there and also have faster drivers, so no glare. Definitely a more subtle presentation. In short, the Elex can get a little excessive, whereas the Quads can be too reserved.
In treble, that tendency is the same. The Elex has some peaks that both give a sense of detail and occasionally come off as abrasive, while the Quads have much more even sounding treble that seems slightly polite at first. With the Elex, cymbals can gain some sizzle and brass can gain some squeak. On the right tracks, the Elex sounds exciting and detailed and energetic, but they are more difficult headphones to pair with genres. That might sound very negative, but really these fairly tolerable issues. The treble on the Quads sounds more even and smoother, letting cymbals be heard without any tizzy or harsh edge to them. The treble on the Quads is much more like a HiFiMan than an Audeze. In other words, detailed and light without being overly accentuated.
Soundstage width and imaging are roughly equal, and both are easier than average to pair with an amp.
Here's the short version. The more I listened to the Elex, the more I realized that this initially exciting, intense headphone is a little too sloppy and unrestrained in areas. The more I listened to the Quads, the more I realized that this initially safely tuned middle-of-the-roader has some real resolution, depth, and finesse. Both great headphones, but one needs a bit of taming and the other a bit of coaxing.
