Soundwise... you will found the MO and the XS sound very similar. Plus, the fact
you can easily turn the MO into the full Motif ES (just load the missing sounds into the user bank
).
Sampling is used to add your own or 3rd party samples into the keyboard,
expanding the sound libraries. Since MO is not a sampler, you just have the sounds
that come with it out of the box - but you're free to customize those any way you like.
Basically, the MO is exactly the same as the Motif ES except it doesn't have the sampling option, it's missing a few sounds
(like I said, those sounds CAN be loaded into the MO), the keybed on the MO is not as good as the one on the Motif
(but it's still better then any keybed on the PSR series or the one on the korg TR) and it has 3 IFX in Performance mode.
Apart from that - they are exactly the same, and if I were you, i'd go for the 88 keys rather
then 61 if that was my only keyboard.