Hmm...that board looks like a knock-off of the MKS BASE series. Unfortunately, the stock board shown only has 4 stepper drivers (with one going to the dual-z connectors). You have two options: Upgrade to a board that supports more extruders (RAMPS, the MKS BASE series, and many other "Arduino-Compatible" printer controllers), OR if you want to keep this board, you can use the servo header (that rectangle of pins next to EXP2 and the Z-endstop connector) to control more stepper drivers and MOSFETs. Do your research, and see which solution suits you.
If you do choose to get a new board, don't worry about connector compatibility or your power supply. Your existing cables' XH2.54 connectors will work just fine with standard male headers (like in the servo header), and pretty much all of the existing printer controllers are just fine with 12V.