D-Link DI-604... it's always worked well, all the way back to the original Xbox system. I had tried that at one point early on in my troubleshooting, but that was a couple weeks ago already. I'll give it another shot and take a look at some settings in there though.
It's really strange. I can't help but think that a fresh windows install might fix the issue, but I'm not ready to do that yet. I did a reformat recently and don't want to have to reinstall everything again on a whim.... plus, if there was some update/software that caused the problem, it's likely to happen again until I know the culprit.
Thanks for the suggestion though.
Edit: Also, I don't know how relevant this is, but when I click on "change advanced sharing options" in the network/sharing center, is says "Media Streaming is On"....
But when I click on the option "choose media streaming options" it brings me to the screen that says "Media Streaming is not turned on. Media streaming allows you to.... (blah blah).... Turn on Media Streaming?"
Sometimes when I go back into advanced sharing, it says right on the main page that streaming is on, other times that it's off... but either way, when I go into the next screen to change it, it says it's off. (like the first screen just doesn't always update/refresh.) Setting it back to on always works, for about 2 minutes of a song.
The whole thing is strange. Perhaps a registry setting that won't stick?