Huge imbalance on digital 3

[Confused]

My guess is that this is a Configurator bug. If you have some free time and are not adverse to a bit of hassle, you could try configuring the slave as a normal stereo 250, then try the Dig 3 input. (or configure the master as a 250 if Dig 3 is a master input) If this works ok, then at least you are narrowing down if the problem is a fault with the amp input or an issue with the dual mono link. If it was me, I think in the first instance I would send a query to Devialet and ask if this is a known dual mono configurator issue.