Backup settings for HDX in the DTC

Where are the settings to create a backup to NAS in the DTC? I have created a shared folder and the NAS is showing as a network share in the DTC, when created from the front panel of the HDX, and as a scannable music share in the DTC. Do I need to promote this to a store on the HDX? When I do, it goes offline; only when I delete it from the HDX does the share come back. I have mapped a drive within Windows which has the HQ, LQ and MQ files in it (from the hdxbackup shared folder). I am nearly there  but what am I missing to create the backup? The backup monitor in the DTC looks like the place to be (under "backup monitor") but the only source drive reference is E:.