My sonic memory is too short to resolve subtle differences between equipment if I have to rewire to test. Therefore I'm thinking of buying something like this Monoprice Dual-Source 2-Channel A/B Speaker Selector with Volume Control and Impedance Matching. This, and other brands like it, are passive devices (no relays) that, therefore, should be using break-before-make switches to protect amplifiers. Has anyone used a device like this for comparisons? Please share your experience, and especially for comparing amplifiers. I can't be the first to think of this, though I can't find a thread on it so I seem to be the first to post about it.