Dear Ton,
just a little additional contribution to your thoughts.
Presently I have Genos, and it took a lot of time to decide for Genos or SX900 (the "baby Genos"), and tested both several times.
I love SX900 and it is an update arranger, a new generation one. This will be precious whenever yo will decide to sell it to buy another keyboard.
SX900 on board speakers are among the best I've heard in arrangers, Their quality is near to studio monitors.
The touch screen interface makes user life tremendously easier, and encourages to dialog with the arranger. All operations and commands are definitively faster and easier. Touch screen became the standard interface for any kind of device, not just in music industry.
Even though SX900 does not have Revo drums, its drumkit (derived from Revo drums) are very close to Genos Revo drums. The general taste of SX900 sound gets very modern, compared to previous arrangers (even flagships).
The portability of SX900 is another factor: to play with a pleasant audio you do not need any additional gear or wires: simplicity.
Finally, the black "dress" of SX900 makes it look professional.
Those concepts, of course, are IMHO.
Ciao
Angelo