I think Sergey has summarised it quite well.
The PX-560 (I own one) is primarily a piano, and IMO a very good one for the price.
It has a graded hammer action keyboard that responds and feels amazingly like a real piano.
I like the colour touch screen too.
And it also has some quite reasonable arranger facilities, whether they're up to the same standard as one would get on the S975 I can't answer, but I suspect not.
In that respect the PSR and Tyros are, I suspect, streets ahead.
But the 560 also has quite a powerful synthesiser on board with what's called a Hex Layer editor.
This allows extensive tweaking of presets as well the creation of completely new sounds.
But it doesn't have the huge range of styles available that one can get for the PSR and Tyros range of instruments.
Somehow I doubt it ever will have.
If you use a lot of styles then I'd opt for the PSR, especially as there are programs offered here for style tweaking.
I create my own MIDI files to practise or play to, using Cakewalk Sonar.
It really depends whether you're after an arranger with a synthesiser style keyboard or something that's primarily a digital piano but has some reasonable arranger capability.
I'm delighted with my px-560, but I primarily wanted a good digital piano at an affordable price. I bought the stand and pedals at the same time.
It's very much a matter of personal taste.
If I had the money I'd have one of each ;-)
Any help?
Colin.