Um... Ok, so don't shoot the messenger here and though I'm not 100% sure on my brief test (I have to head out). I just played two tracks from both OS out of my Mac mini server. Babyface into audiofire 8 into MBP logic 9 48k 24 bit. The tracks were some band limited pink noise - rumble not sure of the file's specs. The other was that Aerosmith Armageddon track drenched in reverb from a show I designed recently. These were obviously played back at separate times but were the exact file. Played back through previewing - space bar on the file- I cannot null them. My nudge value is 1 sample and I can't make Steve Tyler disappear. All I did was change the operating system. I've performed null tests before. There's only 2 things that might be flawed... The babyface settings are slightly different in the 2 OS (or the drivers) or the preview/iTunes playback differs. When I get back from futsal I'll try QuickTime. I'm a bit shocked and thinking it must be me...