TOSLINK SPDIF Optical 5.1CH,Stereo Audio 2.1CH work independently. IF HDMI source play 2.1ch audio, SPDIF & Stereo audio work together; IF play 5.1CH audio, SPDIF work, but no Stereo. HDMI Four input to One output; HDMI input, USB input can switch in sync; 3.5mm Microphone for recording; SPDIF 5.1CH, Stereo 2.1CH audio extractor.