I've been chatting with Ryan about this offline, but for anyone following this, it's important to understand that there are 2 (at least) different powering schemes for condenser mics. "Phantom Power" is an approach that uses 3 wires and (usually) 48 volts. It's what you use with studio condenser mics, etc, with XLR connectors. What is typically used as internal guitar mics in dual source systems are electret condenser mics, which use a 2 wire scheme known variously as "bias power", "a-b power", "T power", or "plug-in power". This is a bias voltage that can be applied to the same wire that produces the signal. So with one of these mics, you typically wire the mic to the ground and ring of a TRS (aka "stereo") jack, and plug it into a guitar preamp that provides the bias voltage on the ring - usually around 9 volts.
These approaches are similar in that they both provide electricity to the mic, but different enough that you can't just use either one - a bit exaggerated, but think of it like the way you plug your toaster into the 110 wall socket, while you power your flashlight from a battery, or your iPhone from a USB cable. All of these are "electricity" and you can convert between them with the appropriate gizmo in some cases, but you can't just plug your toaster into a flashlight battery, etc.
I get asked about this often enough that I created a blog post on my website detailing how I added a mic to a K&K system:
https://dougyoungguitar.com/blog/blo...l-mic-to-a-k-k
it's a *very* easy thing to use if you have the right gear - the right mic wired the right way, a TRS jack and cable and a preamp that supplies the required bias power to the ring. It gets complicated/confusing if you are cobbling together parts that don't work together.