I've noticed the same issue, using a vanilla version of RR. (january release)
::edited out a LOT of -now useless- info::
using the almighty search function and about 2 hours of time, I came across this thread..
http://www.mp3car.com/vbulletin/show...ghlight=volume
it suggests in rrconfig, changing the line"map master volume to control line

for weak sound card) from All Lines to Master or Wave.
Simply Setting it to Master took care of the 0% volume level after adjusting in RR.
Hope that helps someone.