Using 2 routers, Windows network fractured, how to fix?

[listen.here]

I have one of the ethernet ports on my Pace4111N configured as a LAN Subport. In another of the Pace's ethernet ports, I have 1 Windows peer attached. The LAN subport is wired across my house to a Cisco router, to which all my other Windows peers are connected (some by ethernet, others by wifi). The PC plugged into the Pace unit cannot see any of the others Windows workgroup peers. Anybody know how I can fix this? Will using a Homegroup instead do the trick? I know that both routers are running DHCP independently, so the lone PC is on a different subnet from the others; is there some way I could manually assign a local IP address to it that computers on the other subnet could access? I guess I can do this by bridging the Pace router, but then the PC I attach to it won't be behind a NAT, and that will never do. Any suggestions?

[Guest]

Why can't you connect your PC currently attached to the Pace to your Cisco instead?

[listen.here]

>> The LAN subport is wired across my house to a Cisco router
"across my house" is about 60 feet, through the attic. I could run another length of cat5 but want to avoid that if I can. It seems I can: I posted the question to r/sysadmin and got the reply "Should be straight forward to write a routing rule to do what you want." Sounds like I need to learn about how to write a routing rule and what that rule should do!