The Tyros 2 has a different sound set which requires higher polyphony because there are mega voices and super articulation voices. Even if you get to run Tyros styles on the PSR-S500 you most probably will not be pleased with how they sound.

I suppose that the PSR-S500 already has a few styles from the Tyros which has already been optimized and use less polyphony.

You cannot expect wonders from an entry level keyboard. That's why they are entry level. If you like it you'll move to a mid level one and eventually to a top level keyboard.

My suggestion is to get the best keyboard you can with the money you have. You already know that there will be new keyboard announced next month.

So - the choice is yours.

Kind regards,
George