Guess that many of us would like such a function, but sadly these players do not come with such functions from the manufacturers.
However, Rolleyflex have this thread on merging firmwares to enable individual song browsing at:
http://www.mympxplayer.org/merging-f...tml?highlight=
Some works, some don't.
Hopefully someone with good Z80 coding skills is able to re-write a useful firmware to allow song browsing while the music is playing.