Just to clarify, do you have the older PSR-3000 or the newer PSR-A3000?
Either way, you can connect external speakers or monitors to the keyboard's OUTPUT jacks. There are separate R and L/L+R jacks, so you can either use two 1/4" TS cables to connect to separate left and right speakers, or use one 1/4" TRS cable plugged into the L/L+R jack.