The Linksys WAP11 can operate as an "Access Point Client" to another WAP11 acting as a normal access point. This allows you to bridge two ethernet networks while still having an access point to be used by regular 802.11b clients. For your configuration, you could hang one WAP11 off your switch upstairs and set it up to be an access point. Downstairs you can hang the second WAP11 off a hub/switch or directly into the HSX-109 (might need a crossover for direct connection... not sure). The downstairs WAP11 would be set up as an access point client and you'd configure it with the MAC address of the upstairs WAP11.

WAP11's run about $140 in the US. I'm planning a similiar configuration for my Rio Receiver because HPNA has proven to be unreliable in my house and I'd rather spend money than deal with dropping an ethernet cable in the living room.

I believe this access point client configuration is proprietary to Linksys and won't work with other brands, but I'm not sure. Anyone know?

-Dylan