Hi Mike,
you may have two problems:
1. You need to setup your DX 50 to send out NMEA sentences. I'm not quite sure how you do it, but if it is similar to LX 5000 it is under Password > NMEA Output. Enable GGA, RMC and LXWP_ if you can.
2. If you are successfully using SeeYou Mobile with a Bluetooth GPS, the Port settings are incorrect for DX50 for sure. For DX50 you need to change them in Menu > Settings > Input > Serial > Port Settings > COM 1, 4800bps.
Personally, I use two Profiles to distinguish between the option of being connected to a vario (LX160+Colibri in my case) or a CF GPS.