Does the NAS connect to the modem and get assigned an IP number? (will be different than the IP on the old modem). You can check this in the Home Connect app - click on WiFi at the bottom (even though you are connecting via wire) and there should be a list of connected devices at the bottom - clicking on the device and then "Device details" should show the IP address (10.0.0.xx ?). If so, can you connect to that IP to get at the NAS? If the NAS does not show up in the connected devices, you need to figure out how to get it to connect (maybe something on the NAS itself? similar to what you probably had to do before).
You should also be able to log in to the modem directly (10.0.0.1) like you could on the older Hitron (probably 192.168.0.1), where you can assign a DHCP reservation if needed. Username should be admin and the password on the bottom of the modem (unless you changed the password). If you can't figure out how to do that, you probably shouldn't mess with it.
