Same deal here, in fact with the same sound device listed. I primarily use a Xonar STX for sound output.
Sound card:
Audio device: Realtek ALC898
Still an issue in 2019.
Steam System Information only picks up the DisplayPort connector rather than either the onboard sound or the USB sound card that I actually use.
Nothing extracted yet.
Steam system information display only
even if there for example also USB sound adapter and HDMI audio output device.