I believe this is the best way.

The DVR is connected to the main router by ethernet. A desktop is connected to another router, which is connected to the main router via wifi client mode.

Basically: DVR -> Main Router <- Other Router <- Desktop

I cannot make a direct connection to the DVR through the other router, but I can using a USB adapter. But the USB adapter doesn't work well due to poor signal strength, so the DVR software is sensitive to dropped packets, and so I prefer using the other router for that and other reasons.

I'm trying to figure out how set up a static route, on which router do I create the static route, and using luci, what does the interface, target, IPv4 netmask, IPv4 Gateway, and metric options mean?