I may be able to help you, by explaining the X series keyboard/module vs the XD series...
#1. How you choose sounds and styles is one BIG difference. With the X series, all 198 styles are listed on the module with bank A & B (99 in A & 99 in B). To call up a style, you look at the list , choose bank a or b..
...With the XD series, all styles are located under category buttons (latin-rock etc...)... You press a button, look in the screen, use 1 of the 10 function buttons (5 on each side)to select your style...

So overall, navigation is a big difference..

However, the X series has 4 out puts..
The XD does not... left / right stereo

The XD series has the "remix feature", that allows someone using midi files, to remix that GM drum track and use a drum track from an onboard style, to make the midi song have a more "live" sound..
Play a country song , chose a county style and the drum track will have variations and fill ins, in real time... "remix" ....
The screen on the X series is a little bigger and brighter...

These are the 3 biggest things so far...

I'll be back... Dan O'