Probably I don't appreciate enough the fact that I live 1.5 hours away from Moscow and usually I can try most of keyboards at a store. So it seems a bit unusual to me to order something just to try it. Although it's getting really popular here to order clothes just to try them on, but it is usually delivered to a local "office" (don't know the right term in English). Mostly here people prefer to pick up things in some "agency" nearby rather than to wait for a courier to come home. Additionally, we live in a city like in an anthill, so it's more rational this way.
I'm saying it because I can imagine this feeling about whether it's right one or not when you're actually trying it personally. In the same time under a pressure sometimes it's easy to decline everything just for a sake of being on a safe side.
Given that recently you had PA4X and now you gave SX900 a chance, I'm not really sure that the industry of arranger keyboards has a lot more to offer.
Now it's been nearly 2 months since I got Juno DS, I can say that I have some complains, but generally I feel that I need this keyboard and it helps me to do what I can't do without it, but what I want to say is that even after this amount of time I'm still getting used to it, it still feels new to me.
I can't really see what I actually can learn within a day; even two weeks, trying to cover everything, is just stressful and surely not enough.
Meanwhile, thinking about upgrading my PSR-S950, I was repeatedly coming to a dissapointment for two reasons: it would involve significant expenses, and all the alternatives didn't seem to offer a big improvement, sometimes it even seemed as a regression. Even when I listen to demos of SX900 I hear a lot of familiar stuff.
My PSR-S950 in a service now and they called me and said that I had used it so much that they would have to replace a pitch bend and some buttons. So I hope that I will play it for some time and then with some luck I'll get a new SX900 or something, in that case such an upgrade will be justified on a ground of a physical conditions.
So far I have to play my old PSR-3000, while voices are quite dated, there's still something to work with, but it is having them both (Juno DS with 76 keys and an arranger) is what keeping me enthused.
Coincidentally, Zuki also had some dissapointments when he was trying to get a newer arranger and then he just added Yamaha MX61 to his old one and it seemed to work well for him.
Basically, some recent PSR like S970, or Korg PA700/1000 are already TOTL instruments in many terms, and it's hard to go higher when you're already close to a top, and it leaves you to move in different directions.
It's similar to what scientists say about money. Till a certain level more money can mean more "happiness", but after a certain point it just stops working. And it leaves a person to look for a happiness in other things, mostly in building relationships with other people.