Thank you mwillems. Didn't know what "copy bass to subwoofer" did. Then that's settled.
I guess I'm using Asio loopback. Considering I'm using Lynx Asio under "Output Mode" in JRiver. That's Asio loopback when liveloopback is chosen as URL, right?
It definetly works with other programs and browsers. I can both hear the subwoofers playing and I can see in the Lynx mixer that signal is active for the subwoofer channel. Under the Windows Audio panel, I simply chose something I'm not using (HDMI output).
So if Asio loopback works in REW, what do I choose for my Steinberg sound card?
It actually sounds like you're doing WASAPI loopback, not ASIO loopback. There are two key legs in the audio chain:
1) there's the loopback
input into JRiver (which can be WASAPI or ASIO), and
2) Your actual
output device (which can be WASAPI, ASIO, etc.)
The two legs can use different protocols (one can be WASAPI, and the other ASIO, etc.)
In your case it sounds like your JRiver
output is ASIO to the Lynx, that's 2), not 1). It if you're opening live loopback and using your unused HDMI output for the loopback device then you're using WASAPI loopback for the
input, not ASIO loopback (which doesn't require a separate audio device, but does require ASIO-capable software). WASAPI loopback is more flexible because most windows software can't output to ASIO.
So if I'm right that you're using WASAPI loopback, the solution is to choose your HDMI output device as the output in REW using java, not ASIO. That will cause REW to output to the HDMI, which JRiver will pick up on the loopback and re-route to your ASIO output on the Lynx.