So you're about to spend thousands of dollars into a silent piano... and you want to plug in speakers to its output...
I don't understand this. Silent pianos offer the possibility to play silently, and 1) you never needed TRS speakers out or that kind of "improvement" Yamaha adds, because almost any amplified speakers would do just as fine with an adapted cable through the phone output (Yamaha is selling an extra plug to you, what for an improvement!) 2) if you are to play at loud, you don't need speakers, and if you do, because of the noise of the action in silent mode and because of the poor ability of any speaker to amplify a dp decently, you'll have to turn the volume quite loud to get any sensation at all, the sound will be coming from the speakers, which you'll probably set up too far from one another and from the piano to have only the impression you're playing a piano, and mostly what you'll hear won't please you (can't you just use a headphone?) Plus speakers near piano is really a ugly setup.
If you're not to play at loud at all, why are you only buying an silent piano?
If you really want to play the very average Yamaha silent dp (with the new samples but still very average) through speakers, you have to buy amplified studio monitors, Yamaha make some
, many brands do, starting price for a decent solution 300-500$ each speaker. And you'll be deceived. You should record your dp on a cd, and get into a music shop selling studio monitors, and ask to listen to your recording through various speakers to choose the one you dislike the less...
Unless you go for a very expansive professional stage wireless solution, if it only exists, you won't find anything reliable and decent (I guess you'd get latency, parasite noises, poor speakers and sound) in the consumer electronics market.
Could you please explain what need you would have to buy extra speakers to play your silent piano, what situation it would involve, and for what purpose?