I have similar goals as yours with respect to optimized two channel music[;is integratiion with a multichannel system.
I started this thread on AVS about the DLNA format for audio.
http://www.avsforum.com/t/1337255/dlna-dac-usb-dac-is-the-dlna-dac-the-futureI learned quite a bit.... Basically, I concluded that the DLNA protocal was not implemented with enough rigor to pursue for my system.
Moreover, I want to use JRiver MC to organize my media files and control the choice of music for playback from my hard disk/PC. Moreover, Using the android gizmo app or tremote running on another PC, I get the control that i demand.
The new Oppo's now provide asynchronous USB to feed their seperate two channel DAC solution.
If I were you, I would add a PC client to your rack and go with a USB out to your OPPO 103 Asynchronous DAC input. Chances are your DAC/PREAMP USB input is older and not the asynchronous implementation and so it could have a bit more jitter. (I Would love to hear which version sounds best in your hands and how they compare to your disk players). (of course you have a limit on the lenght of the USB cable.
Adding more grist to the debate...
What I don't fully understand is what to do with multichannel content stored on the server. Do you use MC to do the digital processing for 7 channel content and the room correction and base management, or do you send the data to your PRE/PRO or AV reciever and let this firmware do the job?
If you wanted to go with the MC solution, the multiichannel DACs available do not appear to be all that great. So... what is the best way to get the data from your media server to your AV hardware is also not clear to me. Currently, I think that a moderately priced reciever (7 channel DACS and room correction, and base management all built in) is the optimal way to go. I would think that using an hdmi out from your rack PC to the AV Pre/pro or reciever would be the best solution.
I don't know if anyone has compared the JRiver digital processing solutions with the firm ware available in AV recievers with Audessy (or their proprietary room correction scheme). but.... Since the multichannel / movie problem is last on my list of needs.... I choose to muddle along and covet my speaker upgrade (grin).
Good luck... let us know how you proceed!