I have used that ASUS RT-AC66U and it is a very nice router, I don't think that is going to be your problem. The web interface on that router may be able to help you troubleshoot the connection though. You can monitor the current wifi connections, signal strength, and check to see if there are other networks close by that may be using the same wifi channels. You can even imitate the WPS function without pressing the button on the router.
It's too bad the LCS doesn't have web interface that allows you to custom configure wireless connections to your home network environment so that you don't have to use WPS.
I have tried following the progress of the connection on the router, but I don't see anything that helps. The maddening thing is that once when I first got this, it actually connected. I have checked to make sure I allow 802.11b connections, that seemed like a logical issue, but that's not it.
I live in a semi-rural setting, and my network is the big dog around here. I see a couple of neighbors at very low levels, but they're on different channels. I have fired off WPS from the WPS page, it reacts the same as when I use the back-panel WPS button. I also have the latest firmware for the router.
I don't see anything pertaining to the LCS WiFi in my status in the router.