setting up sub via low level input and setting frequency crossover

[thumb5]

I don't believe this is true as i have configured the the sub digital out on my 800 at a lowpass crossover of 80?  

It's not possible to set crossovers for digital outputs on the Devialet. You can only use one or two analog output(s). One for mono and two for stereo.

I think Antoine is right: surely the output to your sub is analogue, not digital?