Hi Will,
Is it this system? https://www.amazon.com/ZOSI-Security-recorder-Weatherproof-Smartphone/dp/B00MP57IOY The cameras can be analog or IP. What do you have?
If I understand you correct you want to keep the system as it is with the cameras connected to the dvr and then connect NCS to the dvr? So the question is finding the URL on how to communicate with the dvr? Can you connect to the dvr from a web browser and see the cameras and get audio?
I found this guide how to access the system from a PC https://support.zositech.com/hc/en-us/articles/115003549927-How-to-set-up-remote-viewing-on-smartphone-and-PC-
I also found this in this forum Netcam Studio and ZOSI NVR/Cameras - #4 by Steve that you can test.
When you have it running from the PC you can use the program Wireshark and analyse the network communication between the PC and the dvr and from there get the URL. Most likely the URL will look like http://dvr-IP-number:port/xxxxx The magic is to find port and xxxxxx.
When you have he URL use the tab for Custom URL to add the system to NCS. It will probably look like http://username:password@dvr-IP-number:port/xxxxx
Zosi seems to have a good support so contact them and ask for the URL.
-Henrik