I don't know the original 2488 and MKII but I have a Neo. As I know the only differences are:
1. Neo doesn't have the tone generator and drums set, it only loads midi files and while you play it sends midi to the Midi Out. Nothing internal.
2. Neo has a Mastering section. So, once you have the mix done as you do on all 2488, on Neo you can "master" the mix.
3. Neo has a nice white and black back light LCD.
4. Neo comes with bigger hard disk. Mine came with 160 Gb while was advertised as 80 Gb. I don't know if previous version accept 160 Gb hard disk.
May be somebody can help with something more I skip.
