You can always daisy chain routers, WAN to LAN. The only thing you have to make sure of is that each is using a unique network. For example, if the PK5000 is using 192.168.1.x, then perhaps make the EA4500 192.168.2.x, or 10.0.0.x.
That said, what many ppl prefer (assuming your modem+router supports it) is to place the modem+router in “bridge mode”. This demotes it to a modem-only. No routing, no firewall, no local network, etc. Just a simple modem. And now the public IP is passed to your router just like any other standalone dsl/cable modem. Some of the advantages include not being double NAT’d and not having to configure multiple firewalls. It’s just a cleaner and easier to manage solution if you’re going to use your own router.