Hi Petr,
If you are determined to switch to Yamaha, I advise you to buy the Genos, the SX900 is not for the Genos what the PA1000 is for the PA4x. Many things are missing, from sound editing to the lack of Sart.2 and the 24-bit construction.
If you just sing, Genos will give you a lot of satisfaction, extraordinary sound, if you want to do other things, especially editing (sound style song), Yamaha, in general, will give you some frustrations by sending you to the computer every time. Similarly, if you are a follower of the 6 CVs for each style: M, m, 7, dim.... think twice, it will no longer be possible.
Unfortunately now the PA5x, except maybe the sound, does not rise to the possibilities of the PA4x whose SH price here is about 1000 Euros higher than a new one before the PA5x.
Good luck!