Hello Ken,
It depends on what you want to do with your speakers, meaning: Is it for mixing, mastering or for listening and enjoying the sounds of your keyboard, or for stage performance?
The Yamaha HS5 are very good - but they are designed for near-field reference sound. So you would use them with a DAW for instance to do your mixing and mastering. During that process, you just want to hear "the truth" - which is very different from wanting to hear "nice".
So you need the right speakers for the application. That is why your Bose earphones sound great - they are made to sound "nice" for listening - but they would be not that great for mixing :-)
Cheers, Roland