Speaker cables is usually more expensive and can be prone to picking up emi, etc., so keeping them short is good. Balanced inputs are good at rejecting noise and interference and are usually a much smaller gauge and thus, cheaper.
I would not solder my speaker cables and inputs to the ncore. If some how they get tugged, there go your amps. If you ever want to change them (you will), you will have to unsolder and resolder. The less you do that the better and you run the risk of messing up the ncore boards. The benefits just don't justify the risks, to me. But go ahead if you are set on it...