Here's yet another clip of text (this time taken from) Yamahasynth.com that shows the MM6 having arranger capabilities just might be true.

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The MM6 Music Synthesizer delivers all that power and more. Drawing on the same sounds of the popular pro-level MOTIF series instruments, the MM6 has a wide variety of dynamic, realistic and just plain powerful Voices to help you create amazing music. The MM6 also gives you total control over your sound, with real-time tweakable knobs, and features special Patterns that provide full backing - drums, bass and chords - for your live performance and song creation. And since the MM6 is exceptionally light and portable, you can bring it anywhere and everywhere your music takes you
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Notice is says "special patterns", and they used the term "full backing". I think that along with pattern controls also support this.

I think people here should be excited about this if it's true. A Yamaha keyboard with Motif based sound engine, real-time control, 200+ arps, 8 track sequencer, and the possibility of arranger control....