AirPort Extreme: Extend only 5GHz Network

I have a Time Capsule 802.11n (4th Generation) set up to extend my WiFi network to our Sitting Room down stairs.

The WiFi Base Station, upstairs in my Office, is an Airport Extreme 802.11n (5th Generation).

Attached to my Sony TV is a Brightech DoublePlay HD Bluetooth 4.0 Transmitter, operating on the 2.4GHz Band which severely effects the communications on my WiFi Network (demonstrated unequivocally by unplugging it from the USB port of the TV).

Can I force the Time Capsule 802.11n (4th Generation) in my Sitting Room to extend the WiFi network exclusively on the 5GHz Band.

I have named the 5GHz Network on the Base Station Airport Extreme 802.11n (5th Generation), and have configure the Time Capsule 802.11n (4th Generation) in my Sitting Room to Extend the named 5GHZ Network (not the Dual Band WiFi Network) but am unsure if the Time Capsule 802.11n (4th Generation) in my Sitting Room is locked onto the 5GHz Band. Is there a way to check this.

Appreciate your help, anyone...

WiFi performance has been appalling while listening to movie audio via the Bluetooth Head Sets, taking many hours to be ready to play an iTunes movie, or play will stall and forecast many hours to be ready to resume. If I can lock the Time Capsule 802.11n (4th Generation) in my Sitting Room onto the 5GHz WiFi network, I suspect I will have this issue sorted.