Your DX5e Transmitter is DSM2, and the AR400 is DSMx, but they should work together.  From Horizon Hobby's website...

quote]<h2>Is DSM2 and DSMX equipment compatible?</h2>

Yes! DSM2 transmitters are forward compatible with DSMX receivers and DSMX transmitters are backward compatible with DSM2 receivers. And because DSM2 and DSMX share the same wideband DSSS foundation, all Spektrum users will enjoy superior range, speed and precision whether they're using DSM2 equipment, DSMX equipment or a combination of both.</p>

It is important to note, however, that the only way to experience the full benefits of DSMX (wideband DSSS plus frequency agility) is by pairing a DSMX transmitter with a DSMX receiver.</p>[/quote]