I have a custom bar top arcade which has menu buttons on a front panel to navigate Emulationstation. I found another bit of configs I needed to place into es_input.cfg:
<?xml version="1.0"?>
<inputList>
<inputConfig type="joystick" deviceName="Xin-Mo Xin-Mo Dual Arcade" deviceGUID="03000000c0160000e105000001010000">
<input name="a" type="button" id="11" value="1" />
<input name="b" type="button" id="8" value="1" />
<input name="down" type="axis" id="1" value="1" />
<input name="left" type="axis" id="0" value="-1" />
<input name="leftbottom" type="button" id="2" value="1" />
<input name="right" type="axis" id="0" value="1" />
<input name="rightbottom" type="button" id="5" value="1" />
<input name="select" type="button" id="9" value="1" />
<input name="start" type="button" id="10" value="1" />
<input name="up" type="axis" id="1" value="-1" />
<input name="x" type="button" id="1" value="1" />
<input name="y" type="button" id="0" value="1" />
</inputConfig>
</inputList>
Sorry for the false alarm. :/