Q1: How to achieve time alignment when comparing 2 DACs at home ?
Q2: How to achieve crossfade between 2 analog signals and how long should the fade be ?
Q3: When you do hard switching (analog time/level aligned no fade available) should it be make before break at line level (not recommended for speaker amps) ?
Q4: When doing break before make; what would be the maximum allowed 'silence' in ms ? The max timing difference between L and R ?
Q5: When designing an AB box that can do this for speaker and line-level inputs the relay types should be fixed ?
Q6: When using the same box for DAC outputs how to achieve time alignment between DACs ? Would that require specific software ? Is that freeware ?
Q7: Is the FAQ meant to encourage folks to test properly at home or to show it is complicated and requires specialized equipment that is expensive/hard to find for the test to be valid (to discourage and think again before one tries) or is it to show that even when you think you AB'ed correctly you still might not have done so. ?
1) it's hard. You also have to get good level alignment. A scope is really handy there. If you're testing DAC's it is possible to use a 4-channel output to the 2 stereo DACS (for instance) and build the delay into the program that loads the audio data into the driver.
2) this can be tough. make before break can help IF you can ensure you don't cause output misconduct. Like you said, no, do not to this with power amps. That is in the realm of relays and best needs short smooth mutes around the relay "click". Yes, this is a pain in the behind.
3) Going to silence in a discontinuity (i.e. a click) is bad news. It might almost be a pot driven by the two (line level) inputs driven back and forth. That would work for low level signals.
If you HAVE to break before make, smoothly mute the input first, and then bring it up again afterwards. There's no way this can be an ultimate test, of course, but it's what you can do that isn't worse. Clicks really throw things off.
I don't know about the second DAC question. Yes, such software exists, no it's not freeware that I know of, although it would make sense for somebody to do that.
As to FAQ - I'd make it a graduated scale, from "just barely double blind" to "as good as you can get". As you have observed, these tests are a pain in the behind.