I’ve had the Hifiman HE4XX’s for about a year now. While I absolutely love their sound (first planar headphones I’ve had) they can feel a bit harsh over long sessions. The biggest issue with them for me is how the sit on my head. They put a lot of pressure on one specific part of my head and irritate to the point of only being able to wear them for sub 2 hour sessions.
I am looking for headphones in the $200-450 dollar range, with a different soundstage and signature than the 4XX’s. Something different, not necessarily planar. Also comfortable and preferably not quite as heavy on my head.
You have a lot of options if you just need something comfortable and different. My suggestion is either a HD600 or 6XX. Though keep in mind they may have excessive clamp until they’re broken in
Depending on what you pick, I’d suggest upgrading the amp to something like a magni 3+. The Sennheiser’s will definitely benefit. But if the M3 can handle the 4XX, it might be fine as is