The SMC appliance (gateway) that Comcast ships with their static Biz accounts, by default, will utilize an IP on its WAN interface, and provide NAT/firewalling for devices plugged into it that have their TCP set to obtain auto...it will hand out IPs something like 10.1.10.100...or something like that. So it acts like any home grade router in that respect.
When you want to use your own router ...and put one of your static IPs to your own router....you simply plug in that static IP/subnet/gateway/DNS into the WAN interface of your own router, ....and plug your routers WAN interface into one of those 4 ports in the back of the SMC gateway.
Or if you want to plug in just your bare server...with that server on that IP address...you could do that, but I highly...highly recommend you don't plug a server right onto a public IP address, stick it behind a good router/firewall with NAT, and have only the bare minimum ports open/forwarded necessary to make available whatever it is that this server does.
If you're running 2x servers...most decent firewall/routers will support multiple IPs on the external interface.
That particular IP (range) address/subnet/default gateway/dns is on the sheet of paper that you got from Comcast when you had your biz account setup/installed.
The last thing is to log into the SMC device, and shut off it's firewall. I forget the LAN IP again..something like 10.1.10.1...(just set your IP to obtain auto, plug into it..do an IP config /all)....
username and password are something like cusadmin and highspeed.
Look around, there's a "disable firewall" checkbox around there.