The "problem" with oriental music is that it use specific instruments and in order to be able to reproduce it You need keyboard with these instruments (voices), or ability to add the missing voices. Yamaha PSR S900 doesn't have these instruments voices installed, and You can't install new voices. All You can do is changing installed voices, but there is no possibility to add new waveforms (needed for accurately reproducing new instruments). For something like that You would need arranger keyboard with sampler (like Tyros, Pa-800, etc).

Second "problem" are styles. Although You can copy oriental style to non-oriental keyboard (from OS700 to S700 or S900) it will not sound the same because OR700 have additional drum kits not available on S700 and S900. I am not sure, but it seems that it's not possible to have user defined drum kits on S700 and S900.

Bottom line is, if You buy arranger with sampler (much expensive than standard arrangers) and user drum kit available, You can play any kind of music You like. But if You want to spend less money, buy oriental arranger, it's a bit more expensive then equal non-oriental version, but cheaper then arranger-samplers.