I tried pinging the AP but I only have the MAC from the base of the unit. Strangely it isn’t listed as a connected item as any of the routers DHCP clients or in the log.
now that does seem weird. To confirm – you are pinging 192.168.11.254? If it’s not responding at all then something somewhere in the setup is evidently wrong and so the AP obviously wouldn’t be extending your range as it’s not on the LAN.
At that point I fear I’m right out of suggestions and sounds like your antenna would be a good bet.
Just out of interest though, if you have the SB right up close to the router when it’s wireless, does firefly appear as a server on the display? Equally, can you confirm that firefly appears as a share in iTunes? And how far away from the router before you lose firefly?