If your cable modem has a LAN-type output on it, then you can connect that to a router (NOT a modem-router) and a wireless access point to that, and you have the makings of a system.
You will have to do some shuffling of IP addresses - if the cable modem is 192.168.0.1, then the router will need to be 192.168.1.1 or whatever.
That's how my system was for a long time, till I lashed out on an all-in-one device. I think it was better the old way.