OK you're right, the order has to be correct.

1-xStatsClass
2-xLabel
3-xPopup
4-Everything else...

Still don't know if xStatsClass can load automatically or if it needs to be explicitly stated in theme.rc. i'll test

According to xPopup readme, xPopup gets it's info from xLabel.
That's why there's an 'xLabelLight' module. That's so you can hook info from xLabel without actually using any xLabels.