To be brief: When using Synthesia with my workstation keyboard (which naturally has hundreds of sounds), it doesn't output the piano sound that I necessarily want.
For example, it will play the sound assigned to "Acoustic Grand Piano" on my keyboard, but in fact, I want the sound "Studio Grand Piano" (which is the default anyway). This is mostly personal preference, but I've also noticed some weird distortion issues mostly when previewing songs. I have a Casio wk7600.
Using a different piano output with keyboards
When describing problems, always mention your OS and game version (shown at the bottom of the title screen).
If your keyboard has USB or MIDI ports, there is a tremendously high chance (>99%) it will work with Synthesia. See what you'll need on the keyboards page.
If your keyboard has USB or MIDI ports, there is a tremendously high chance (>99%) it will work with Synthesia. See what you'll need on the keyboards page.