Well, my experience with the HE-350 since they've arrived was extremely unpleasant. I was part of those first backers back in March and waited... and waited... and waited... I even watched Zeos review them so I could try to formulate a hypothesis as to what they sounded like.
And after they arrived and I had them on my head, I started to experience tremendous pain on my upper head. The pads were so tough and the clamping force so mighty that I couldn't bear even to have them on my head. It was so bad I couldn't listen to them how HiFiman wanted them to sound like!
So I decided to break the leather headband strap (on the ends so I can put it back later) in order to bend back the top metal headband to get rid of the clamping force. On the HE-350 thread, people told me to "use the dt 770, 880, 990 pads. They work great!". And I'm sure they would, except that I LOVE my dt 990s; they are my favorite pair of headphones and I didn't want to have to buy another set of those pads nor peel off the ones I have in order to give this nightmare more air.
Luckily, Dekoni made and dropped a set of the Fostex x Massdrop pads in sheepskin leather and I had them. Perfect fit on the Hifiman ring for the headphones. Then I attached them, and they felt comfortable. No more pain.
After listening to them that way, there was a lot more bass with what I considered cheapo desktop dell speaker treble. It just seemed muddied and out there and then I realized I basically cut off half of the driver with the new pads. Every violin I heard was just awful. (tbh what I did hear before the pad swap made the violins sound awful). I guess they're ok now, but they aren't my first, second, nor third choice for listening to music. That and the cable is just too short for my desktop uses and I haven't been bothered to find a longer one. Once the Fostex x Massdrop Ebony TX-00 get in, these pads will move over there and then I might change them again with others.
So by comparison, when all I had to do was open box, put on headphones and feel the second most comfortable pair of headphones that I have, and then just listen without complaints, the Lasmex win everyday of the week plus Sundays.
Sound wise, I still like the signature of the 350s, but I think the Lasmex has better overall tone quality. Lasmex puts out nice violins, whereas I think the 350s have the worst sounding violins of all my headphones (lindsey sterling violins across 10 pairs of headphones). Lasmex has more space in the soundstage than the 350 from what I've heard and my perception of soundstage. Lastly, imagining is about the same. If it weren't for those problems when I opened the box for the first time, I may think that they are closer than I've put them here. However, I 98/100 I would take the Lasmex stock over the Hifiman modified. YMMV
Note: I do have a huge head, and I was actually buying the 350s so I could try out their fit and finish before going after their higher end planar models. Also, my pair still has a problem with the connection with the right ear dropping out occasionally. I would send them back, but I like to tinker with them now.