Soumendra, if you are recording in a studio, you shouldn’t have to use mic cut/pass filters. I don’t use FCPX, so I can’t comment on that, but perhaps you could post an audio sample, so we can hear it.
For audio sweetening, I use a few programs, depending upon what needs tweaking. 1) Vegas Video Pro (it has great audio tools), Cool Edit 2000 (no longer around, but you might find a download somewhere), and Audacity (free). Cool Edit 2000, does a very good job of removing difficult audio problems like air conditioning noise by using sampling of the signal in a noise only area, and then using that to subtract that sound from the whole file.
Bob
Bob