well you know what, I owned both Gr07 classic (the slight weaker version of GR07 bass) and MA750I. TRUST ME!!! they have 0 similarity lolllllll
GR07 is clear, balanced, detailed and crisp. MA750I is full, adjusted towards lower end and to me, just wired sounding. Like I have w4r now, which is also considering a not so bright IEM. But the dramatic difference between w4r and MA750I is the amount of details I can hear. With w4r, I feel like I am sitting at the front row of a concert, you have everybody on the stage, they are bit far from you, but you hear everything and such sound is mild, so you can listen to music for a long time. MA750I is like you are listening to a concert with grass ticket or I don't know, like listening to it on the hallway. GR07 is a typical balanced IEM, so you are basically standing on the stage and in the middle of a band.
Hopefully this will give you a sense of what you are getting if you decided to buy MA750. I personally returned it after a week of listening. Tried very hard to like it but just couldn't