Having the exact same issue - I can get all my old devices except my Slingbox M1 to connect to my new router. The setup stops at the part where it kills your internet connection on your laptop and it's supposed to make you enter in your network credentials through the slingbox, but it never gets to that part.
I've already hard reset the M1, tried the WPS button, etc... The setup app isn't very helpful and brings you into a lot of endless loops (with ads I have to watch over and over again while trying to set it up!).
Any help would be appreciated!