Sorry to the group for yet another post, but I had a conversation a few hours ago on this topic, as it relates to non MB topics. Anyway, there is simply no tangible difference between a 16 and 24 bit FLAC file, and the same applies to a standard and Mastered for iTunes M4A file. The same also applies to a CD and a HDCD or any of the sorts. A CD is played in a CD player, which has DACs that do the work. DAC meaning Digital to Analog Converter… I believe Burr Brown are still the top class. This goes far beyond, I think, of MB, but it most likely ends up at 16 bit anyway. Then you have the quality of the cable, the preamp, the amp, speaker cable, then speaker. Or I guess the output jack, headphone cable and headphone transducers. But there is more difference between a iTunes M4A and a amazon MP3 than there is with a 16 bit and a 24 bit FLAC. I just speak honest facts, although I would love to believe that a 24 bit FLAC is better. It is just not the case.
I will make a disclaimer, that on a second generation+ remastering (the FLAC is a mastered file after all), there is in fact a difference. I doubt that is in scope of MB though. But as is well known, you cannot master a master without being destructive.