Please (again) see
http://ohnosec.org/drupal/node/48 for all the gory details of setup with chan_usbradio. If you use chan_simpleusb the RX procedure is a bit different: Generate (with a service monitor) a full quieting 1kHz tone at 3kHz dev with no CTCSS. At the OS CLI type radio_tune_menu, adjust the reading for 3kHz. With a RTCM the procedure is pretty much the same except you have nice indicator LEDs right on the RTCM.
Transmit is pretty much the same regardless of the interface. Turn of any TX CTCSS. Press *989 to generate the reference test level tone. Then measuring with your service monitor set the dev to 3 kHz.
Is there a way to turn their volume down?