Denon DVD-3910 Universal Player; help with digital

Hi. I recently moved my Denon 3910 universal player into my listening room to use its DVD-Audio and SACD playback capabilities. My reference digital player is the venerable Cambridge Audio Azur 740C vII upsampling 24-bit 192/384 unit. The 740C has digital optical & RCA inputs so you can use it as an external DAC (it has dual Wolfson 8470 DACs run in dual differential mode and extremely high upsampling software). It was my intent to use the Denon's optical digital output to transmit the raw digital DVD-Audio signal and (perhaps?) the direct SACD signal through the 740C's DACs (the Denon has a "Pure Direct" feature). I also have the Denon connected to my preamp (Musical Fidelity A3cr dual-mono unit) directly through high-end analog interconnects (the Denon does have triple Burr-Brown 24-bit DACs per channel in its own right). The DVD-Audio signal passes through the digital connection some of the time with some DVD-A discs, but often the digital output is silent and the signal passes straight to the preamp via the analog cables. ????!! Since the 3910 is in my audio room now, I don't have a monitor to play with the onscreen setup menu. Before taking the 3910 into my audio room, I used the TV in my den to view the onscreen setup menu to enable the digital output, and also to change the multi-channel default settings for DVD-Audio & SACD 2-channel playback. If anyone has experience with this popular unit, or otherwise has advice, I'd really appreciate it. Thanks!!