And about Digital audio output? I dunno if both are the same.
There are 2 potential pathways to send digital output out of the laptop and to an external device.
1. The HDMI port is for sending out a digital video and audio feed to a TV, monitor, or other device that has an HDMI input port. Normal the audio that goes out through HDMI is whatever audio is associated with the video. I'm not sure if it would work out to use the HDMI port as a conduit for general audio purposes. I would go with a usb device rather than try to use HDMI.
2. The usb port can send out a digital audio signal if you plug a usb audio device into it.
[By "usb audio device", I specifically mean a usb device that contains a DAC (digital-to-audio converter). If the device does not have a DAC then Windows will not give you the option to send the audio signal through the usb port.]
The device that Speedstep linked to is an example of a usb audio device. It has a DAC and also has a pass-through for S/PDIF as per your original question. There are many more kinds of usb audio devices available.