Unfortunately, even any test which used one of these boxes would only be valid for those systems which left this switchbox in the chain as a matter of everyday use. Otherwise, the results are contaminated just by the presence of the switch box. Of course, if you did a DBT ABX trial comparing your system with switchbox versus without the switchbox and the results were then not significantly different versus chance, then you could then use the switchbox.

I guess we're back to just listening to see which sounds better to each of us?