From the ALSA wiki
The Audigy LS does not have a master volume control. For analog output, use "Analog Front", "Analog Rear" and "Analog Center/LFE" for volume.
For digital output, Enable "SPDIF Out" On=Digital, Off=Analog. Use "SPDIF Front", "SPDIF Rear" and "SPDIF Center/LFE" for volume.
For the 24-bit 7.1 card there is also an "Analog Side" control and a "SPDIF Unknown" control, you can adjust those volumes for the side speakers. The 7.1 card doesn't have a master volume control either but you can get good results using the various software mixing options in programs. To differ the volume of your center and LFE speaker just split the control using for instance Kmix and adjust the right channel for LFE and left channel for center speaker.