Besides my SX700, I also have a PSR-S670 which weights 3.5kg less compared to the SX700. That's why I always use my s670 when I need to move around. Tyros styles play very well on the S670, but OTS settings need adaptation if the instruments are missing. So if you find a cheap second hand S670, this could be a good alternative.
But if you have the budget, I fully agree with Bogdan and Brian that the SX600 is a better choice: same weight as the S670, better sound and capable of directly reading registrations of the Tyros (my SX700 can handle them so I guess this also applies to the SX600).