I agree with Serman, the Dunu DN 1000 is a step up from the MA750 soundwise. Build wise though the Dunu is quite large and the MA750 is the more comfy by far imo.
DN1k is quite bright, so highs can be quite sharp (but good quality) and the mid bass is slightly more emphasised than sub bass.
MA750 goes a bit lower, but bass quality isn't as good. There is a slight veil to the mids in the RHA also, so the Dunu is more detailed. Both have good soundstage.
Both offer good sound and as Serman said the RHA has a great warranty, and tips can make all the difference. I like foam tips and for super isolation I wear SpinFits.
You should look into the Trinity Audio Delta. They are a company set-up by some long time members of Head Fi, Fit wise it's very comfy and theycome with 7 filters which change the sound signature ever so slightly, without breaking away from the overall sound. So more/less bass, treble, etc. It's very musical and good for many genres.
https://trinity-audio-engineering.myshopify.com/products/trinity-delta