You are on the right trail, you need to set the ips to the same subnet from the end of the chain backwards.
change the cube ip, change the sub-router ip (this device should actually be a hub, not a router), change the gateway ip, change your computers ip.
You lose the network when the ip doesn't match. I think your issue is that the second router is a different ip from the first router (your internet gateway).
Change the second router to match the cube default, then change the first router to match, then change your computer, it will work