I asked this on the Audio Engineering thread on CS but the thread is dead so:

How do u fix muffled audio in fl studio mixes? When I listen to my mixes in my Focusrite audio interface, they sound more clearer than when I exported my songs and listen to them with regular headphones.

Bump

If i was you id google this question and search it on youtube

The DAW itself shouldn't be muffling the mixes. You may be mixing stuff too loud which is squashing the vocals. Also try sweeping with a narrow EQ to find any boxy or unwanted frequencies. I generally boost the high end of the vocals (about 10k up) so it sounds more shiny and cuts through. This also adds some air to the vocals

Export Settings .. Just Go Highest ..

If Yiu Dont KNow What to Do with the Highest You Weak .