1. It is too hard for me to enunciate.
— This can mean either a) Enunciation in general is too hard for me, or b) Enunciation of this particular thing ("it") is too hard for me.
2. It is too hard to enunciate for me.
— If this meant anything, it would mean that someone else was attempting to enunciate on my behalf.
3. For me to enunciate is too hard.
— Put a comma after "me", and the meaning is as for 1a, but with more emphasis on my particular difficulty in enunciation.
4. For me is too hard to enunciate.
— Not used.
5. For me it is too hard to enunciate.
— The meaning is again ambiguous, as with #1, but with more emphasis on the hardness of my particular difficulty.
6. To enunciate is too hard for me.
— as 1a.
7. To enunciate for me is too hard.
— Put commas round "for me", and then it is as #6, but with special emphasis on "my" difficulty.
There may be other interpretations, however, from other posters!
Student or Learner