How are you hearing no difference?

Some very good points made here. I take care quite often to have a friend come help blind test; I also compare over time, and get my wife's "golden ears" opinion until she gets annoyed (humor).

I understand and agree that certain components will sound similar, especially DAC's. I've had to do some very careful listening to reveal the smallest of differences. On one occasion, the difference was so slight, it came down to a two second section where I could hear a difference of a faint bongo beat that DAC A presented with more percussion than DAC B (about the 6:56-58 mark on the song "Morning Mist" performed by Ahmad Jamal).

If you think that two components sound the same, then you need to keep listening until you hear the difference.

I'll admit that sometimes the differences can be so small they aren't worth mentioning or not meaningful enough. In the DAC comparison I described above, that difference had meaning to me, small as it was.

The issue is who would need such a test and why. I do not think it is useful for an individual audiophile for whom the only determinant is "what do I like better". 

n80 - I don't find it useful when someone describes two components sounding the same, that's my point. It just makes sense to me to find the difference if you've taken an interest to compare. Notice I'm not saying "better", a subjective term but sometimes useful.  I suppose someone can argue that the term "different" is subjective as to the skill of the listener, the equipment, if detectable, etc.