Interesting conclusion to this. I'll post what I found in case others run into this. I had picked up a FlySky Tx and Rx and hooked up the Rx this morning. I bound the Tx and set everything up then tried the kill switch....nothing. That's when I realized I had the dip switch in the 2 channel position so i moved it to the 3 channel position and it worked perfect.
Then I wondered about the Spektrum DX2E and the SR310, so I reinstalled the SR310, hooked the kill switch to AUX1, and pressed the bind button. The kill switch works perfectly.
So I found out it did not work with the Spektrum stock combo using the 2 channel instructions and the y-adapter, but it works fine if you use the 3 channel instructions and use the bind button to kill the engine. I did start and run the DBXL to confirm proper operation, rather than just trusting what the LED flashes on the super bee were telling me.