The yamaha ydp 143 has 2 phone inputs which are used for adding headphone jacks mainly
I believe you mean headphone outputs because according to Yamaha and other dealer websites this board comes with two 1/4" output jacks.
Headphone jacks are almost always stereo connections, so you are getting stereo not mono. It's possible that the reason you are getting ...
Use whatever the studio has.
Use their engineer to set it up.
If they already have a studio kit, consider using that instead.* Their engineer will be very familiar with it.
The time to be learning how to mic up a large drum kit in a room you don't know with mics you don't know is not now. You will not get it right in a week, maybe not even a month.