Let me see if can help. Maximum, you are tring to use a multiport router at both ends to attach a DVR, and another device that will send data only for alarms right? If so, I think I know the problem. When using a web safe router, inorder for the DVR to work properly, you must direct the DMZ to the IP address of the recorder, with that configured, the other ports can also use the internet bandwidth, but if you use the math, the DVR is probably taking close to 100% of the avail bandwidth, which means if you try to take another device, assign a statis IP from the routers and go the other direction with data only, it should work, it will just slow the DVR data rate down.
Make sense?