Hi David,
I have an upgraded 5800 which comes with the ATKIS RC8000 and 8001 docking station. It has a USB input and (although I haven't done it myself) there was a code update dnld a couple of years ago. If you ave a 5805, I would think those codes are already loaded.
Regarding streaming A/V, the sound card on my PC has an Optical output for digital as well as analogs. I presently use Windows Media 9 as the player for my HDCD coded discs as Microsoft is a co-dveloper of that format and has incorporated it in WM9.
Since all the digital inputs on the Denon are assignable, I've chosen CD, OPT 2 for this connection. My PC is also connected to my HDTV through the video card for the video part.
From what I understand any Denon receiver with assignable inputs can be used in this way. If your PC does not have a digital output the L/R analogs can be input and also assigned.
My old PC sound card had an optical output but it was a minjack so I had to buy a minjack to standard opt cable, which at the time was almost as expensive as the sound card.
Anyway, the Remote for the Denon mentioned above does allow for dnldable code upgrades.
Peter M.