The problem is that many streaming web services (probably for copyright related reasons) only output sound to the system default sound device (bypassing JRiver). Netflix in particular is a big offender, and it sounds like Pandora does the same thing. This unfortuante decision on the part of streaming services has two main consequences:
1) If your system default audio device is different than your output device in JRiver, you'll get playback in the wrong place (on the system default) and
2) It completely bypasses JRiver's audio engine (i.e. JRiver has no control over the sound).
If you don't use JRiver for signal processing or DSP, etc., and your soundcard has a normal windows driver you can resolve the problem by setting your system default sound device to the same one you use in JRiver.
The other solution (@kstich, this is probably what you'll need to do) is JRiver's software WASAPI loopback function, which effectively "steals" the output routed to the system's default soundcard and re-routes it through JRiver's audio engine. Unfortunately, that means you might need to use a browser or app to play the wed audio (rather than starting it in JRiver's internal browser). The good news is, it will allow you to pass the web audio through JRiver's audio engine. Here's how:
1. To use the loopback you have to have another soundcard in the system. You can use the motherboard soundcard. Nothing is actually connected to it, but the drivers still need to be installed. You might need to turn autosense off in the motherboard drivers. Many people have the Realtek HD Audio on their motherboard. Disabling front jack detection in the Realtek HD Audio Manager is what actually enables the analog output from front and rear outputs.
2. Set the above soundcard as 7.1 (with fullrange speakers) and as the default soundcard in the Windows Control Panel.
3. Set JRiver's Audio output [to whatever your soundcard is]
4. Before turning on web audio in the browser, put JRiver in loopback mode by going to File > Open URL and enter live://loopback [or open live, WASAPI Loopback]
(adapted from an older post by mojave to make it applicable to the current JRiver)
There is also an ASIO line in method described in this thread:
http://yabb.jriver.com/interact/index.php?topic=88217.0But it requires external software to work, whereas the wasapi loopback works out of the box as long as you have an unused sound device set as the default (which both of you do).