Thanks guys for your answers so far, they are very important to me.
If I lived in USA I would have bought a Tyros2, no doubt. Here in my country the decision should be taken considering the most suitable for me and if it is worth the price of the arranger available.
If I buy the Korg Pa500 I am afraid I could find quite similar sounds to the Korg Tr I already have. I know I won't have many extra styles but I would keep the PSR 1500 with thousands of styles and I could use the Pa as a module or vice versa. But are those Rx sounds so amazing? Are they articulated sounds like the S.A. of Yamaha? Is it the Korg Pa EDS sound engine different from the Korg Tr HI synthesis?. If I trade my PSR 1500 paying 2,000$ extra dollars for the PSR s900, instead of keeping my PSR 1500 and buying the Pa500 (1,595$), I would only get 90 high quality voices (I am not interested in all the extra functions nor polyphony) but I would also have ONE arranger not TWO one on top of the other what is harder to control.
I know it all depends on personal preferences but I need the listen to those who know these keyboards.

P.S. Frankieve I am waiting for you to open a new branch of your business in Buenos Aires.