Sam, Aftertouch allows you to modify the sound or effects by pressing a little harder on the keys. It is editable, meaning you can assign different functions to it. Most of the time aftertouch is set to vibrato, and you can add it by pressing harder on the key. I noticed on the 8000, the default settings require you to press fairly hard on the keys to activate the effect, but you can set the 8000 so that less pressure is required, then save your settings in registration memory.
P.S. I totally agree that the 8000 is far easier to learn than the X1, after having played both of them for several months, five nights a week. The X1 has vast capabilities and great sound, but it's hard to learn, particularly if you're not a veteran Solton player.