Got some hybrids and let them burn in for just a few hours. They're better but still a ways to go to do it for me. I don't think the hybrids are the best tips for me. FXT90 stock large tips were working great for me with the FXT90 but I lost them along with the headphones. I will try to get my hands on my mom's pair since she uses medium.
I like the bass on these. That was what was really lacking for me in the FXT90s, but in every other regard my memory of them was a lot better than these. They just had a beautifully natural, crisp, and slightly airy timbre. So far the IM70s sound "good" but comparatively muffled and congested. The lack of treble sparkle is my main issue. Snare drums sound like "F" instead of "P". Instrument separation, too. I listen to a lot of symphonies, and pieces by Shostakovich, Mahler, Bruckner, etc. are very richly orchestrated and it pretty much sounds like a thick mess most of the time.
I would like to clarify though that despite all these complaints I wouldn't say I'm disappointed... just not completely satisfied. I definitely believe in burn-in though and probably need to find other tips that suit me better. I do remember really liking my FXT90s out of the box, but they got a lot better over time. I never burned them in per se but I used them regularly for almost two years and they had opened and warmed up a lot.
If these tighten up and improve in transparency I'll be really happy because I like their big robust sound. It just gets all muddled up when there's a lot going on. When the music is thinner they sound very good.
For some positive comments: I think they're pretty comfortable and I've experienced basically zero microphonics. Today I walked with them and heard no thudding with my footsteps and the isolation was pretty decent. In between tracks I could hear the outside and it seemed like average/poor isolation but when the music was on at normal levels I didn't hear the outside. They're driven super easily too.