There are a few options to hitsounding.
Option #1:
You could listen for drums and other strong sounds and double click on the circle it is on, and add the hitsound
Option #2 (What I prefer):
You could create a "hitsounding diff" and map circles to strong sounds and drums, then use a hitsound copier to copy it into your diffs.
https://osu.ppy.sh/community/forums/topics/131540