The Kaces 9kb dimensions are:
44.5" x 17" x 6.5," closer to the Width 1,003mm (39-5/8")x (17-1/8")x (5-7/8") of the PSR-S900. There's room for the music rest, accessories, sheet music, power cord.
I put the mic cable, a/c adapter, and headset in a tupperware right next to the keyboard and all the other stuff on top of the slice of foam, and it fits as snug as a bug. The buttons and LCD are very well protected because they are covered not only by foam, but by the other stuff.
As everything goes on my dolly, I don't need inline wheels on my gig bag. Even though I suppose that they would be convenient for just rolling the keyboard a couple of feet.
Beakybird