I'm sorry anon125 (anonymous?), I don't ask you the age because I cannot to verify it, this is the last post to which I answer you. Who, usually subscribe oneself to this forum it does for 2 reasons mainly: 1) he have a Yamaha keyboard; 2) he desire to buy a Yamaha keyboard.
I will dwell on the second case. You are free to ask anything and we are kind to answer you. But of all the questions you asked, you never asked the right questions to decide what to buy or because to buy.
Often superfluous questions to which you could get answers semply just by owning the keyboard, and not extrapolating manual pages always asking superficial things, what is the use of an SX900, what means this, what means that, last as you get an agreement of 9 of this post. Before buying the SX900, I waited more than a year but I didn't ask absurd and useless questions, I documented myself, I saw videos on YT, I asked for about strengths and weaknesses , I decided to buy it, when I could I did it. Then, with the keyboard in my hands, I asked the members of this forum, the doubts or problems I encountered in the use, but before, I read the manual, carefully, and I saw other videos.
The way you do questions doesn't make sense, have you ever owned a keyboard? Do you know how main chords are made, before asking how 9 chords are made? I doubt you will ever buy the keyboard, as I doubt it is so naive and innocent, for my part I will not waste time replying to your posts. the other members they are very polite and patient. Maybe you have the best intentions in the world, but I don't like to feel (I repeat FEEL ME) taken for a ride and, I'm sorry for you, but you cannot learn to drive a car knowing how an engine works or reading the instruction booklet.
Aquila uno