Do I need a microphone and sound card to amplify a live instrument? Mic directly to the active roland kc550 keyboard speakers can?

You can connect directly to active speakers without using a microphone amplifier. Sound quality, if the microphone and musical instruments at the same time from this Roland speaker output, the sound quality is really difficult to ensure perfect, the best is the instrument and the microphone are separate independent speaker output. But if it's just a simple show on the street, it's not a big problem. This speaker is much better than those square dance pole speakers.