Some of your questions
Sorry I will not be able to answer all of your questions; however I own the 1920, and can tell you yes, you can have both HDMI and coax/optical-fiber out. Right now I have the hdmi plugged directly into my TV, and the fiber audio going to my denon receiver. Both the TV and the receiver can play audio from the disc.
To get the video upscaling from 480P, you must use HDMI.
Now in terms of the digital processing, my understanding is that by sending the signals via HDMI, Optical, or digital coax; the video signals (hdmi), and the audio (hdmi/fiber/coax) are all kept in their digital forms, so no processing is being done by the DVD player. If you want it do the DAC processing, use the analog outs on the DVD player.
Hope this helps.
Lonwa