Logitech 540Z headphone in on volume control don't work...

Hello,
Can anyone help me figure out why I can't get my
head phone input to work on my Logitech 540Z 5.1 speaker system
I'm running Windows 7 Ultimate just upgraded from Win Co and I just installed
the Audigy 5 RX sound surround works but my headphone input for Logitech volume control does not work...Why?
Can anyone give me some suggestions please!