The analog Line Output does double duty as a Toslink digital output. You need an optical cable with a mini-Toslink connector on the B2 end.
With either of the digital outputs, the volume is at full level with no control over it by the B2. And you won't get the distortion that you get with the analog output maxed out. However, if you use the equalizer, don't max out the sliders, as that has been reported to cause noise even on the digital outputs.