[CentOS] Sound with headphones on: Streamaudio perfect but youtube and system-config-soundcard silent

This afternoon, I bought a pair of ear plugs (the large flat kind that
hook onto my ears).  Plugged them in to test and they work perfectly.
I'm listening to streamaudio.com as I type this.    However, when I
tried to watch a youtube.com video (my wife exercise dancing) just
silence. She had the same video on to test and the sound was fine on
her box. Then, I tried system-config-soundcard and with the volume set
at 100%, just silence. Does this have to do with lower voltages coming
from youtube.com and system-config-soundcard or is there some other
explanation  and a cure? TIA....