What evidence is there that we hear Ultra Sonic audio?

[b3lieve]

FLAC is not a universally useful format. There are few to no "FLAC players". You won't find many car CD players that can handle FLAC. Throwing a CD in a DVR or DVD player with FLAC won't usually do much. Etc.

But a properly prepared mp3 is just fine. There is very little difference in audio quality from my mp3's and FLAC for all practical intents and purposes. The FLAC would have the same results, just a bigger file.

well flac is just another lossless codec anyone can convert to their liking. m4a lossless is 100% compatible across apple devices for example. however, as you've explained the way you do your authoring has no loss so i'm happy to leave it at that.