Best way to A / B test amps? Use a switch?

Hahaha.. Pretty funny and I'm not saying you "forget" a blatantly obvious sound difference. We're not playing in that field here. Audiophiles are obsessed with the slightest nuances and to believe that your superior hearing memory is immune to certain biases is naive.

Everyone knows it's BY FAR better to A/B test with instantaneous switching than relying on memory and what you think you heard.  

Thanks for the other replies.  Unfortunately, I'm not up for building my own.  I would have thought there was something practical on the market already.

Very good points.  Some of which I have considered but not enough.  

I still think the audiophile thinks his aural memory is much keener than it is and not susceptible to audio forum interference/influence.  But, you're right saying that the "over time" part is also very important.  And there are downfalls to switching as well.

The other part of the issue with me personally is I don't have time to deep listen for hours on end and my environment changes quite rapidly.