Not much difference between the two except the ES has a few more sounds and a little bit more ram. But the ram isn't really important unless you are using the Motif as a workstation, like arranging whole songs and sampling in it. If you were looking at getting one but were tight on funds i'd look at getting a motif 6 or ES rack. You're pretty much getting the same thing, I use both daily so trust me. Now, if you got chips to splurge just get Motif ES and all the expansion packs you can get. Its kind of like having a Benz S430 vs. S500, not much of a noticeable difference, both are great boards. If i'm not mistaken they are the same board, the ES stands for "Expanded System or Extra Storage" can't remember which one though.