HI Spalding

The technology you mention stems from the 70s, and has been advanced over the years to make it more realistic with more type of instruments, (It originally only really worked with organ voices) the first to user it was Lowry Organs and they called it AOC (Automatic Organ Computer) to which they held the patent.

Over the years manufactures have advanced it to include exactly what you describe, (Hence the multiple settings in the Auto chording feature) however it has nothing in common with the active real time multi split/layer system used in the Roland AXR card or VSTi (The auto chording feature is fixed) which have algorithms to achieve a far more realistic sound.

If you look at the DVR VSTi that is mentioned in one of the posts you will also see why a hardware arranger has no chance of being able to perform the operation without additional hardware. (Look at the computer specs required just to play the sounds in DVR)

Bill