cassp: Huh?
Sorry, I don't agree with you. While a synth, along with drum machine, can make a good performance pair, especially when configuring & playing the kb in split mode (with bass in LH and playing comping chords/fills/melody in RH, and of which I occasionally like to play in this style myself), even the best synth and a drum machine together, cannot match what is the 'primary' feature of an 'auto accompaniment' arranger: 'full' instrumental auto-accompaniment (bass, drums, keyboard, + other backing instruments). Only a true arranger keyboard will provide, while played live, a 'complete' rhythm section backing arrangement. - Scott