Regarding the HDMI port, at the rear of the ReadyNAS OS 6 products, this port was inserted for future use. At the time of writing, HDMI use is not currently supported.
Can I plug my TV into HDMI port?
You could, but there would doubtfully be any activity.
Further information:
You can monitor the Forums for updates in the coming months.
Doc # 7008 Rev 1.1 February 2014