It is likely not the number of drivers involved, three-way, two-way, that makes the difference in what you are hearing.

Most keyboards with built-in speakers use an INFINITE baffle design. This is not ported but a box where the speaker is placed that has no other air relief port to the outside world. When the speaker cone is pulled into the box by the signal, it compresses the air inside the box a wee bit and that compressed air actually helps the speaker cone return to its normal position. The opposite applies when the speaker cone is pushed outwards, a wee bit of a vacuum is created, which then helps the speaker to return also.

Some keynoards have small ports in their interior speaker enclosures as well, a bit of tuning for bass response, but most I've encountered use the Infinite Baffle arrangement.

The Infinite Baffle will typically favor the midrange of the audio spectrum a bit more.

That midrange peak alone can yield the sonic illusion that the speaker has a better sound when used in the nearfield, which is what is happening when you are seated at the keyboard in the playing position. Problem with that is that you are the only one likely to be able to be in that nearfield of the built in speakers.

You could try to duplicate that sound through any reasonable amplification system (PA, Instrument Amp, etc.) with the use of an EQ and sculpting the spectrum such that it favors the midrange area a bit more than the FLAT setting, but be advised that this is NOT a condition that will also work well with mics and singing. So don't use a Master EQ if your amp system has to do the mics as well as the keyboard. You might try a separate EQ inline with the keyboard's output and your amp/mixer's keyboard input such that the EQ only affects the keyboard's sounds.

And a well-designed two-way system should be able to do the job just as well as a well-designed three-way system could. It is not the number of drivers.

HTH,


--Mac