I have a similar setup and it works. Here's my info in case it helps. AirPort Express 802.11n 2nd gen running firmware 7.8.1. It's joined to my 5Ghz network us

I have a similar setup and it works. Here's my info in case it helps. AirPort Express 802.11n 2nd gen running firmware 7.8.1. It's joined to my 5Ghz network using 802.11n. I have my home wifi configured with both 2.4 and 5Ghz networks and the AirPort Express is aware of both. Not sure if this makes a difference.