You will not find the address of your Profilux but you can reserve an address to set your Profilux to.

SO you have 3 computers attanched to that router so 3 addresses are already take.

I'm sorry I do not know every router but typically there is a Status page that will tell you who is connected from that page you can tell what IP addresses are used and what are free. As suggested I would guess that 192.168.1.199 is a safe bet to be free why not start with that