
Keyword is "STUDIOS"
"They also feature a range of drum, guitar, bass, keyboard and other musical phrases built in, minimizing the need for complex manual MIDI data programming. Complete compositions can easily be created with just one finger. Of course Yamaha keyboard know-how acquired and refined through years of experience offers feel and response that provide optimum musical control and comfort for smooth production."
More info on Yamaha's site
here. Under the specifications and features I see reference to a 342 type arpeggiator which I'm guessing is the implementation of the above.
"The KX Series features a built-in arpeggiator with more than 500 pre-programmed phrases. Select an instrument and style, then simply hold the appropriate notes on the keyboard to play or enter the MIDI phrase data. For example, a guitarist could create a demo by entering all the required parts other than guitar by using the arpeggiator, and then overdub the actual guitar tracks. The KX Series makes it easy to create background music for your home page, backing for solo practice, and much more."
You can find the arpeggio list type
here. Now we just need a built in multitrack step sequencer.