You could always place a script in your startup scripts to adjust the volume defaults, something like this might work:
#!/bin/sh
# Script to set up the level of volume at startup
aumix -v 50 -b 50 -t 50 -s 100 -w 100 -p 50 -l 0 -m 0 -c 0 -x 50 \
-i 50 > /dev/null 2>&1
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