technicsplayer, you're probably right. The digital out would bypass any analog conversion (assuming they build it that way, which is not a given).

Why didn't they make the Motif an arranger? There are probably many reasons, here are two that come to mind:
Price would be prohibitive for many people.
"Professional Workstation" image of Motif would likely be tarnished (to those people who consider arrangers to be "unprofessional").