Hi - i initially bought an SX900 as it is shorter ( being a 61) than Genos, as I only have a short space at home to keep it, genos was just too big.
Have to say the 900 was very good, but I went down to an SX700, as I soon realised I did not need the difference in spec between the two, which is unusual!
I have loaded any additional styles and voices I needed easily and the memory for me on the 700 is more than adequate as i usually save to USB anyhow, and IMHO it is really the same board without a loop function and I dont need mic. harmony myself. Plus despite on-board speakers not being quite as powerful as the 900's the 700 is pretty darn good and I use an external Logitech speaker system with it anyway, so it is just as good.
The good think about the SX is it is just SO compact and all the controls are well placed and just so handy. for using on the fly.
(Genos was all over the place - you need long arms...lol )
I never get that with a 76 or 88 why the **** they need to run the controls to the far ends of the cabinet/keybed??? when they can manage to compact a 61's controls in to a much shorter reach just in line/above the keys!! and work around internal speakers which is great for a user. This is where the SX like the PSR range scores in my book.
I clawed back WELL OVER £500 moving down a gear from a 900 to 700 and have bought a Korg i3(to sit above my SX700 ) with the price difference.
I am DELIGHTED with the combination for the single investment of less than the price of an sx900. at under £1300 in total for the 2 NEW boards. ( less than the price of a well used Tyros!! )
I had got used to Genos and the SX works in just the same way, same touch screen on the SX ( smaller ) and same OS....sure you will love one whichever you choose.
I have never had such great value for money out of a board as i have found in the SX700 ...Bang for buck, it is amazing, plus as I say, having the Korg i3 with it with all the bread and butter korg voices and styles it is just the icing on the cake!!
Just a few years back, this level of kit would have cost a fortune!
Keith
ps...just in case you interested in the i3 - here is a demo ...it is available in black to match the SX
https://www.youtube.com/watch?v=BTspYoYaVKA&feature=emb_rel_end