As people have said, you need a dummy plug plugged into one of the Powerlink outputs to fool the unit into thinking it has speakers connected. You can make this yourself if you want - it just needs a DIN plug with a 4.7kOhm resistor connected between Pin 4 (Speaker on) and Pin 2 (GND)
Then the digital output will work and full remote control will be available (although not volume, obviously).
I ran mine like this for a few years into a Yamaha preamplifier's digital input and it worked perfectly.