well i couldnt understand wht u said, I have xp also but i cant find wht u said, any how, to find each speakers volume, u can go to control panel then sound and audio devices and under volume tab choose advanced, now under speakers tab choose 5.1 surrond sound then ok
now double click on the volume icon in the taskbar then choose speaker volume and u will have the volume for each speaker.
about the spdif it works with me (i use the coax cable) only if there is a song or a game or and thing else running.
if u have the same speakers when u connect the coax to the speakers it will tell u in the speakers lcd no digital data but as soon u run a song or something else it will work
by the way u have to make sure under volume icon in the taskbar then advanced that the spdif interface is ticked to make it work with the coax cable
if u need more help just say
cheers