You don't need FLAC or 320kbps to notice the difference between junk and good headphones. Frequency response is noticeable when listening to FM radio, and will be noticeable on 128kbps mp3 as well. Not all headphones sound the same (duh), and the ones that came with my Note 2 sound pretty bad regardless of source and bit rate, they're cheap headphones and perform like you'd expect for freebies.
These will be a big improvement to anybody replacing cheap headphones with them, even if you only have 128kbps mp3 rips.