I've been playing with a few technical signal chain things. Seems to make a big difference in sound.
1) Much of the sound of an e-piano was in the amp and speakers. The EP sound coming from the built-in Yamaha speakers just don't convince me there is a real EP and amp in the room.
Just recently IK Multimedia released a free version of Amplitube. It is a pretty good software simulation of a guitar amp and speaker. This software runs as both stand alone and as a "plug-in" on both Windows and Mac.
Turns out you can run either a physical DP or a software virtual instrument through Amplitube and, I think it "nails" the sound. I listen to the sound of a Yamaha DP on my studio monitors and it sounds like it is playing through a Fender Bassman and I can even dial in a bit of spring reverb or tube overdrive sound
Good news is the zero cost. IK gives you the basic software which is "good enough" but they have a system where you can buy extra features for $5 to $20. They hope to make money that way. It might work, I've already given them $15.
It works as a plug-in too. I can use a MIDI connection to play a software EP and then route the sound to the Amplitube plug-in and then to the monitors. Aplitube has a few nice effects too, like stereo chorus and stereo reverb as well as Emulated studio effects like compressors and so on. So you can really shape the sound of an EP. The simulation is ultra detailed, uses a physical model of each vacuum tube and other parts.
I think the weak point of most EPs is the amp/speaker simulation. Aplitube gets this part dead on right even annoying details like tube "hiss" and reverb spring crashes. The software was designed for guitar players but works well for EPs too.
2) second thing: impulse response (IR) based reverbs are designed to reproduce the sound of a space like a concert hall or even a shower stall. but it turns out they can also do thinks like model the sound of a grand piano's wooden case and lid and the wood stage floor. I've just found out that the tools to experiment with this are free/cheap and I've already got most of what I need. Likely many of you do too. To record your own custom IRs you need a monitor speaker and a microphone, something many people have already.