I'd suggest setting up a *BSD-based firewall/router/gateway/AP to front for your network, and just disperse the blackbox access points to maximize your coverage. A primarily *BSD-based solution (OpenBSD preferred but the other BSDs can do the task equally well) will give you security, stability and enormous flexibility in terms of what you can implement, relative to sticking with the SMC APs.
Wireless networks made simple: (OpenBSD)
Wireless Networking: (FreeBSD)
Have fun.