Comment 37 for bug 986817

Thanks for the log. Looking at the log, PulseAudio seems to do the right thing. It first tests input:multichannel, which succeeds, then output:multichannel, which also succeeds, but when then trying full duplex, we get an error back from the kernel:

I: [lt-pulseaudio] (alsa-lib)pcm_hw.c: SNDRV_PCM_IOCTL_PREPARE failed (-16)
I: [lt-pulseaudio] alsa-util.c: snd_pcm_hw_params failed: Device or resource busy

As a result, "Multichannel input" and "Multichannel output" are available, but not the combination of both. From your point 4) it sounds like the gnome audio settings react a bit strange/buggy on this. I assume you have checked both "output" and "input" tabs, right? If you change from "Multichannel output" to "Multichannel input" and it disappears on the output tab, it should start showing up on the input tab instead. Otherwise you can use the pavucontrol to change profile (on the configuration tab of pavucontrol).

But the main question is why full duplex fails here - are you getting full duplex to work with other applications (that are not using PulseAudio)?