I definitely believe you, but this means either the Presonus is broken, or something else is going on with the way you switch the A/D/A in and out. Again, if you had to do five generations of A/D/A before you could hear any change, that's at odds with what you now report, that even mom hears it after only one generation.
The point danbronson is making is that from the moment he got the PreSonus, he was listening to everything through the D/A converters. Every track he recorded was being played back through the D/A on the PreSonus.
He heard the big difference when he bypassed the converters entirely, listening to the mic before any conversion happened.
The fact that he didn't hear much difference when he ran it through the A/D and D/A multiple times doesn't negate the results. If the converters were (for argument's sake) rolling off everything below 100 Hz, then it doesn't matter how many times he ran the signal through the converters, he wouldn't hear anything below 100 Hz, because the converters themselves were affecting the sound. He only heard those frequencies once he took the converter OUT of the signal chain.
I know it's not as simple as a filter at 100 Hz, but I think the point still stands -- the converters made an audible difference to the sound.
Either way, let me know when you guys do the double-blind test. I'd be interested to hear the results.