Can I combine 9v500mA with 12v375mA, or would it be better to combine 9v500mA with 9v500mA?
No, you should not combine two different voltages together. Yes, combining two 9v 500mA outlets is the best option.
Does the pedal sound better at 12v than it does at 9v?
No, it makes no difference sonically with a digital pedal.
