This is really promising. I don't trust myself to do soldering, so this could make a DIY cable accessible to me. However, I do have a question -- have you done this yourself? Is the sound quality equivalent to a soldered cable? I have seen numerous comments on other websites saying that using the screws instead of solder can negatively affect sound quality because the connection is not as "complete," for lack of a more technical term.
You can use the pole versions of the speakon connector instead with the spade connectors if you don't like the screw down versions. I find them very convenient, and they are used in Pro Audio performances all the time.
Does your headphone negatively affect sound quality dramatically since it isn't soldered to the amp? Exactly. As long as you have a good crimp (and you can use thicker gauge wire too), you won't notice a difference over soldering. I have my speaker mains and 2000 watts of subs running through the same connectors.