It is easy to tell if JAM is connected correctly by the status of the LEDs on the top panel. If it's green, you're ready to rock, and the light becomes your input level indicator. If it turns red, the signal is too high and needs to be lowered a bit with the control knob next to JAM.
Blue - JAM is connected but no software is using it. power save mode.
Green - JAM is connected, ready and working with the software.
Red - the level is too high.