The RDX is a network device, you see the web interface here https://youtu.be/0Bvzh_RsBPM?t=1236. It looks like each drive or volume can be a iscsi target that could be connected to the nakivo server and then a backup repository could be created on those iscsi drive targets right?
It is something that i may be interested in but i would like to see a "how to" video on the process on your youtube. I saw that you have a "how to" video on amazon ec2 backups (which is old now by the way)