well what I see not for using gsync you need that full display port cable like I linked above for how I see it
heres what this guy said
''I have that exact monitor, it has 2 modes, g-sync and normal. G-sync use only DP, while normal mode use HDMI/DVI. You can connect 2 cables at once, which is what I'm doing. One cable to DP to use g-sync, one to DVI to use normal mode. You can change mode simply by clicking on the monitor.''
https://www.reddit.com/r/pcmasterrace/comments/38wqxg/hdmi_to_displayport_on_gsync_monitor/