NVR that can record from a cheap DVR?

I have a couple of cheap DVR's with 4 analog cameras connected to them.

They are generic no brand devices, but they use the CMS software that is compatible with the cheap ESCAM IP cameras from the likes of deal extreme etc.

I would like to get a NVR that can connect to the 4 streams of each DVR, and display all 8 in total cameras on a single HDMI output and record all of them to an attached harddrive, as the DVR's location means they dont offer much in the way of security and extending the cables to a more secure location would be costly.

After seeing the software is the same as that for my new escam cameras, I bought the escam DVR hoping it would connect to the DVR as well, but while it finds it in a scan of the network, it doesnt actually show anything or give me anywhere to choose the input etc from.

I am not opposed to changing the DVR's for something better than the cheapest one I could find locally, but changing the cameras to IP is not really an option at this stage because of both access to the cameras locations (height) and also cabling being hard to swap out.

Last resort is to get a PC running the CMS software and leaving that on all the time, but a lower power, smaller, easier to hide away solution would be better.

You can do that with both Hikvision and Dahua. You could replace the DVRs with Hikvision/Dahua units, and then use a Hikvision/Dahua NVR (or hybrid) to record from the DVRs.

The DVRs would basically be working as encoders; they would not even need a HD installed (but installing a HD would give you redundant recording, on the DVR and on the NVR).