it would be nice if they implemented a capture device for Linux & Mac though, I don't think there's anything stopping them (except for having a developer free to implement it of course)
I agree; I can't speak to Macs, but it might be less work on Linux than the devs are contemplating, especially given how easy it is to register virtual audio sinks on Linux. I've successfully fed audio between programs with shell redirection before
. If JRiver implemented audio input on stdin, writing an alsa or pulse sink that would do loopback should be ten lines of config or so. I tried to abuse the webstream playback to hack it in, but the roundtrip latency going out to TCP and back again was ruinous.