The G61 will show Dolby Digital, DTS, or maybe even 2 channel PCM as the stream type. Per the specs of the Sony display:

DIGITAL AUDIO OUT (OPTICAL)
Digital optical jack (Two channel linear
PCM: 48 kHz 16 bits, Dolby Audio, DTS)

This will sound fantastic. HD audio is really only relevant on Bluray sources and there are a lot of choices for dual HDMI output players which will allow you to pass 4k to your display and the PCM decoded HD audio track to the HD621. Many of the Bluray players also decode DD+ and output as PCM if you really want the few extra bits.

558.2 amp, Meridian A500 speakers, M2500 sub, Director & Explorer DACs