ABX; you really need to do it to understand.

[Shadrach]

I think that the way the question is structured, you've made what I call the Procrustean Fallacy, that is, assuming there is a single answer. There isn't.

Step one, before all else- define specifically what it is you're trying to test. Then a reasonable protocol can be developed for that specific question. It will NOT be the same for testing other things.

The things that others are mentioning here (e.g., level matching) are just basic controls, things that are necessary but not sufficient.

There are many variations on ABX testing. For something a straightforward and non critical as audio, for the majority it's going to be a curiosity driven endeavor. When it comes to design assessments then I would agree, a specific goal and more stringent test conditions are necessary.
If I hope for anything from this thread it's that people will try ABX out at it's most basic level and what's more, enjoy the experience.

 

[andreasmaaan]

I've got lots of time for Rod Elliott. He's been one of the few rational voices in recreational audio over the years.
I've built a few of his projects.

I haven't built his stuff, but I completely agree about his credentials and contribution.