The successful call was with a headset. When I unplugged that "Stereo Input" became unavailable and only "Multichannel Input" was and input did not work any more. Trying to switch back to the headset on the next call caused a massive interference for the other attendees. (Right now the "mute" button on the keyboard, on the <F4> key, is stuck and always lights up, i.e., I cannot toggle mute any more. That changes when I plug in the head set, and changes back again when I unplug that.) Do I assume correctly that for calls "Stereo Input+Output" and a headset are best for the time being? If there is any way I can help (test or otherwise), please let me know.