Solved/Maybe/Try this - When your DST6501 isn't WPA2/AES even though the web interface says it is

Posting, in case it helps anyone else.

Problem: Even though the web interface on my DST6501 was set to WPA2/AES, my network analyzer said WPA2+TKIP, and my Apple product warned of "weak security"

Solution and/or "Try this": Click the REBOOT button from within the web interface of the extender.  OK, make sure the security is set to WPA2/AES also, but clicking the REBOOT button is my key point.  (Yes, I realize the router looks like it's rebooting when you just change security settings too.  Nonetheless, try clicking REBOOT too.) 

None of the other things I tried worked, including unplugging the device, counting to ten, replugging it in, or changing security to NONE then back to WPA2/AES.  Clicking the REBOOT button on the web interface worked.  Logic says this step shouldn't be necessary, but in my case, it fixed my problem when nothing else I tried worked.   Good luck!