I have the Amigo II USB soundcard from Turtlebeach running Renoise 2.8 on Ubuntu 12.10. In other applications I can turn the volume down in the Sound Settings of the OS and they play more quietly through the output of the USB soundcard. However, Renoise always outputs at full volume through the USB soundcard. When I use the headphone jack, changing the volume in the OS works. My current work around is to lower the master track volume so I don’t blow out my ears. However, with this system I can’t master the levels of the finished track using the USB soundcard (and my headphone jack is now broken). I should mention this happens whether I am using JACK or ALSA for audio device type.
I figured out a solution. I installed Jack Mixer from the Ubuntu Software Center and then routed Renoise to the mixer, turned the volume down on the mixer, and routed the mixer to the out on the USB soundcard.
Now I can also use the Mixer and Jack to run other apps along with Renoise.