Thanks for the replies guys.
I'm outputting my audio through my AMD 5770 GPU via a WASAPI connection over HDMI to my receiver. This is the only audio output that my computer has that can support passing 24/192 audio, of which I have quite a few files.
I used to have my GPU sending a stereo signal to my receiver, but I recently began using JRiver (and my computer) as a movie source since my blu ray player broke. Because of this, I needed to re-configure my GPU to be able to send a 7.1 signal when necessary (movies). However, I still want to maintain good 2 channel performance for my music. The issue though is that the GPU will not allow me to output 2 channel only from JRiver, as it is requesting a 7.1 source to pass on, since it's now configured to run in 7.1.
As things stand right now, I have three zones set up:
1) "Player" Zone
This is the "default" zone that came with JRiver. I have this one set up as my most pure audio zone. It outputs audio over an exclusive WASAPI connection via HDMI to the receiver. I have the DSP output set to not do any upmixing or downmixing. This mode produces hiss on the center and surround channels while playing a two channel source through my L/R tower speakers. I can get the hiss to go away by: a) turning off the amp that is powering the center and surrounds, b) switching my receiver to "stereo" mode (2.1) from "direct" mode (which plays any and all channels that are coming to the receiver, in my case, a 7.1 signal from JRiver, even though the center and surround channels don't contain any audio).
2) "Music" Zone
I created this zone with all the same settings as the "Player" zone, except I did not make this one have an exclusive connection. I wanted this mode so that I could still hear audio from Windows, web browsers, etc. This is the zone that I use most frequently. It has the same hiss issues as the zone above, and I can do the same things to get rid of the hiss.
3) "Movie" Zone
This zone is also WASAPI, but not exclusive. It takes any source and, using JRSS, it creates a 7.1 output. This works flawlessly, probably because it is "covering up" whatever hiss may or may not be there.
Any help or advice that you can offer here would be appreciated!