Martian,
I am not sure what you mean. Why would you twist the 4 wires into 2? If you want 12 ga wire, just buy 12 ga wire.
Yes, the speaker must support this. If you look at the back of a speaker, you'll see the binding posts. If there are 2, it's not to be bi-wired. If there are 4, then you can bi-wire it. So, yes, two wires leave your amp, and 4 wires enter the speaker.
I think everyone would agree you should keep the components, especially the amp, as close to the speakers as possible. It is always best to keep wire lengths shorter.
