Bogdan said, "Yamaha products that a keyboard owner might be interested on are mainly studio monitors, PA systems, and maybe some small mixer (i.e. if you wish to attach additional instrument)."
I agree. That sums up the entire thread.
I might add that choosing the correct speakers depends entirely on what you use your Genos for. I'm a stage player and need decent speakers for small to medium crowds. Hence, I spent $4,000 on two Bose Pro 8 speakers.
If you're a home player, you have a HUGE selection from which to choose. Try out various speakers and be sure to audition them in your home. Don't rely on an in-store demo. If the store doesn't have a way for you to demo them in your home and then return them, go to another store.
Most of what you hear from any speaker is room response. After the speaker produces a sound, that sound becomes the property of the room. If the room is not too reflective, you can get by with a wide range of speaker choices. A subwoofer is probably a wise addition. The Genos line has excellent bass response, so not including a sub is a waste.