Since Devialet digitizes the analog inputs (line level or phono), it's probably best to use the digital output of the BCD. Otherwise the signal will go through the BCD DAC's -> Devialet's A/D converter -> Devialet's DAC.... With that said, it doesn't hurt to experiment, as you can pick analog inputs sampled at 96 or 192. However, I would suggest using the AES/EBU over the coax connection unless you had another source in mind.
I've heard the 400 at a dealer and was rather impressed with digital sources and the ability to digitize your vinyl. At the time of the demo, they didn't have speakers that were listed under the SAM configuration option. I guess that's where Devialet integrated amps really shines.
Jim