I see some similarities with the previous posters. I was quite satisfied with the S770, a very nice keyboard. Unfortunately, it had too little expansion memory. Hence the switch to a nicely priced used S975. Also a fantastic keyboard! Now that the SX900 appears to have even more expansion and user memory, it makes it very attractive. When I had the Genos, I really enjoyed working with a touchscreen. Glad that is also on the SX900. The Tyros 5 and the Genos both had 76 keys and took up a lot of space in my (small) home studio. It turns out that 61 keys are enough for me. I already have trouble finding the right key, so less is better ;-)) I rarely use the +/- octave key. If necessary, I save it in a Reg.mem. The weight is no problem for me as it always stays in the studio. As I already mentioned, the 3-R Voices, Joystick and 2 pedal connections are very welcome. I don't know the Chord Looper and Style Reset, but it is a nice bonus. I have no problem with the keybed, allthought it is a bit loud. The SX900-keybed seems to be slightly better. All fine. I hope once aftertouch is coming to the SX-line?
Just like @Ekurburski said: nice gift to find a SX900 under the X-mas tree! Fingers crossed ;-))