I know most people don't want to hear this- especially after spending a ton of dough on a Stage or Nord Piano- but I have about $3500 into 2 speakers and a di/preamp. Can you get a good sound for less money ? Of course. I'm picky though.

A pair of Yamaha DXR8 or 10s, or EV ZXA1s, or even some of the ever popular QSC K10s. The latter is not a favorite of mine with regards to piano sounds and jazz. You might try some of the entry levels of the RCF-the 310/410As.
Since your keyboard is very portable, I would audition these speakers first hand with your Stage before deciding. All the aforementioned speakers have line inputs where yon can go direct without a mixer. I prefer a preamp stage, as to my ears, it softens the digital sound of the piano and makes it less harsh.
Bottom line-allot as much $$$ as you can for quality speakers. Money well spent. You invest once and there's no upgrading to the "newest model" 3 years down the road.