It may be useful to try one of the more powerful WiFi routers. I had good results in a long 2500 square foot house using the E4200.
Today I would try an EA4500
»homestore.cisco.com/en-us/Router ··· od.htmor
an E4200 if you can find them.
The other good choices I have read about are the ASUS routers »www.asus.com/Networks/Wireless_R ··· /RTN66U/
»www.asus.com/Networks/Wireless_R ··· RTAC66U/
One off the wall solution might be Open Mesh »www.open-mesh.com/
Using a OM2P
»www.open-mesh.com/index.php/prof ··· -us.html
, you could add additional devices by plug in to electrical power outlets to get to your destination. It is strongly recommended that each device be protected by a small UPS if your electrical supply is subject to surges or sags. The network can stay up long enough for orderly shut downs if you have a power failure. I have been told that the absolute maximum is to use 3 OM2Ps, 2 hops, in any direction. You can go in multiple directions, say North, East, South, and West, but use no more than 2 additional OM2Ps to mesh with the main OM2P connected to the modem in any direction. So you could have a 9 device system. I have used other mesh technology and that advice is good from my experience.