The price you paid means nothing for longevity or support. You paid for an expensive Network Attached Storage device. Released in 2010. The mere fact that you can or could run Plex from it, does not mean, nor should it ever mean that it is a truly suitable server. However, you can setup a device far better suited to being a server, and use your NAS as the storage.
Your device was rendered obsolete in 2016. See announcement in this link: ARMv5, PowerPC, and ReadyNAS ROS4 no longer supported starting with Plex Media Server 0.9.17.0
