Ok, that gives an answer to my question, thanks. It sounds like that preamp that you are using has more than enough gain, which can have its own issues. The most notable one is that you are getting to your volume kind of early in the knob rotation. Then again maybe that os ok with you and doesn't addressed. It is just that with more available knob rotation you have finer control over the volume.
So the power supply that I encourage for this type of project is the AMB Labs 011. It is more than capable of providing the requirements of a Korg build, and can provide multiple DV paths if needed, such as in a balanced design.
Sorry, I don't have links to this but here is the circuit board atop a chassis that I am presently using.
