Baz, you could use a small mixer to use more than one mic with the Pa3X. It could be a simple line mixer or splitter as long as you are happy with the same e.q. and effects on both mics.
If you want true control of more than one mic, including e.q., effects, etc., then you'll need a mixer. I think you will be stuck using dynamic mics for both, unless you use a mixer that has phantom power.
You can control start, stop, pitch bend, sustain, etc. on the Yamaha from the Korg. Just check the manuals and create a midi set.