The XX isn't out in the wild yet, so it's unclear for sure.
The Hifi Man 4XX is a very "fun" headphone. It's decently bassy (especially for planar drivers), and is very V-shaped, meaning vocals are very recessed (e.g. Steely Dan vocals, which are already pretty quiet, sound even further away). It is not objective at all, and the V-shape also makes it so that a lot of mid-range details actually feel a little lost. This is even driving them with a Magni 3, which is plenty of power for it.
The 58X, on the other hand, is fairly flat, but like most Sennheisers there is a definite emphasis in the vocals, albeit much less with these headphones than, say, the 6XX which rolls off the treble to make the vocals even more pronounced. They are not exactly reference-quality headphones, but I've actually used them for mixing because they are very detailed and help me pick out mistakes.
Overall, I find myself using the 58X as my daily driver. The 4XX I enjoy very much, use them a lot for "fun" listening if I want a different listening experience, but I find the 58X just as fun, if not more, and it's a lot more detailed.