I use a separate 5GHz channel on my APTC, but I do leave the SSID to be the same as the 2.4GHz SSID.
I don't know that it is using the 5GHz signal (well for every device on the network). But if I wanted to know, on a Mac I would hold down the option key while clicking on the WiFi symbol in the menubar and it would tell me at what channel and frequency the Mac is connected.
Maybe I can fix that for you.
Code:netsh wlan show networks mode=bssid
The channel setting listed under the SSID should give you a clue as to which band that particular SSID uses.