Headphones on the dtxplorer are only coming out of one ear. Is there a way to pan it to both ears?

Yes, what can be done is to get a headphone socket( you will get to buy the inline type fully covered) Make sure that the female socket if wired with the pins across the channels connected in series with a 10 ohm/1watt resistor and connected together to the wire to the heaphone male socket which must go to your drums kit.
Now the headphone you have if this is a one side type, you must get a regular stereo type and plug into the female socket.
You will now hear both the channesl equally.The reason why a sincel side is preferred is to listed to the music through one and hear your playing on the other. but I would also have preferred to hear both lightly than one side to make our perception oriented.
I am also a drummer by hobby but I prefer the accoustic types.
Happy drumming. Please dont forget to rate my advice.

The Yamaha has stereo output through the headphones, so I suspect there is a problem with your headphones, or headphone jack. Try the headphones on another device to see if they're good.
To check the headphone jack, you will have to partially disassemble the unit to check that the contact prongs are not sprung, and that they are making contact when the stereo plug is inserted.
You might try spraying the jack with electrical contact cleaner, and working the plug in and out a few times, since it could be dirt or slight oxidation restricting the signal.
Good luck, hope this helps, and thanks for using FixYa.