So... I'm not crazy about the PX-330 sound (it's just a band-aid DP). Long and the short - I want to send the DP through some type of EQ before the speakers. I was looking into mixers and found that I have to spend more than $200 to get something with a real EQ on it. I got to thinking about just buying a stereo graphic EQ to put before the speakers. ....
If all you need is EQ, buy the EQ box. A $200 mixer is pretty much the low-end for good quality mixers and they have many features you don't need. The stereo unit will have much better (less) self noise.
But if budget is an issue you can use a computer. Run the audio through a good audio interface box. You can buy a PreSonus "AudioBox" for $150. There are other good brands too for about that price. Then you run a DAW on the computer. (Apple's Garage Band would be ideal for this.) Inside the DAW are many different effects like EQ and impulse response reverbs and compressors. These are mostly very good quality. Loop the sound through whatever chain of effects you like. Many of the DAWs, like garage Band have presets to bring up a signal chain with setting that "work" for common use cases like female vocals or acoustic instruments or whatever.
I've also noticed the reverb on most DPs is primitive at best. The software reverbs are 100 times better. Pianos really do need some reverb to make them sound like they are in some kind of room.
I've found this is about the best thing you can do to a digital piano. The output of most DPs is just like a close-mic feed from a recorded acoustic piano and what engineer would simply dump the mic straight onto a recording?
Of course you can buy hardware effects boxes like EQ, limiters and compressors but few pepole outside a big studio do that and even there people now prefer software many times, mainly because you can change the settings later after a recording.