How to make network external HDD?

Question

Hard disks

Actually there is a Zyxel Keenetic router, which distributes the Internet to all devices. There is also an IconBIT XDS73D media player connected to an external hard drive. The player is connected to the local network via an old TP-Link TL-WR741ND v4 router (DD-WRT firmware) configured as a client.
The player itself easily accesses the Internet (there is a built-in browser). You can also go from a computer (Win 7) to the web-face of the player. And through ftp from the computer HDD is visible.
But here in the local network the device stubbornly does not want to appear, and, accordingly, the hard drive is not visible either. DMZ is configured on TP-Link, that is, as I understand it, there should be full access to the player (and to the HDD), but for some reason not. What am I doing wrong, and how can I still configure the external HDD connected to the player to become a network one for the computer?