we have been using SME 5.5 and now 6.0 for the past 1.5 years on RR with our provided Cisco cable modem.
We use it with dual homing ethernet, one going to our network switch, the other to the cable modem. installation detected the onboard NIC and the PCI NIC fine.
You can give up on SME but you'd be missing out!
We previously used Appleshare Mac servers, Cobalt Qube2 servers, and Microsoft SBS and this has been the most robust and reliable for our needs.
Good luck!