I should probably clarify that the 5GHz signal doesn't go away, it's just that the connected devices report having no internet. I'd have thought it was more an issue related to my ISP, except that the 2.4GHz devices still have internet access at the same time. Since the 2.4GHz router is set up...
I want to utilize the USB 3.0 port without using USB 2.0 mode, and without interference to devices using the 2.4GHz band (which I was experiencing with regularity). To do this, I decided to disable the 2.4GHz radio and instead use a spare router (ASUS RT-N10P running FreshTomato) in AP mode...