You need a route from 192.168.10.0 to 192.168.1.0. I would just put the hub on 192.168.1.0 (same net as router 1). Otherwise, you may be able to just add a route locally (on the Amiga), but I think your hub is actually a router/bridge so you may have to do it there.
Edit: saw your second configuration is what I'm talking about. Not sure why the PC would work, but not the RS232. Sounds like the gateway address is different from the LAN ports to the RS232.
Edit2: BTW, don't trust pings for tests. Edge devices could have ICMP replies disabled.
