1. ALAC is Apple’s version of FLAC
2. No sonic difference between ALAC and FLAC
3. 24-bit/96khz is better than 16-bit/44khz CD
4. 24-bit/192khz is FAAAAR better than the 96khz version - higher resolution and increased dynamics
5. DSD is single-bit vs PCM that is a much closer replica of the original musical signal
6. Storage is so cheap that file size is irrelevant
Apple may make some compromises somewhere to accommodate the relatively limited storage space on iOS devices--and that's why I think the new Apple Lossless format for music digital downloads will be 24-bit 96 kHz sampling rate.
Actually,audio resolution is totally a function of bit width, not sample rate. At 16 bit, the resolution is 2^16 or 65,536 possible levels to reproduce the music. 24 bit is 2^24 which is over 16 million different possible levels. 32 bit gives over 4 Billion. Of course, 24 bit files are 50% bigger than 16 bit ones. Another point - dynamic range is totally a function of bit width.
Sample rates over 44.1khz, at their most basic level, make no difference. I know this is heresy. The design of anti-aliasing filters can have an effect, but generally, sample rates above 44.1 are a waste of space - unless you are mastering for bats. Do a search for double blind tests 44.1khz vs 96khz. Even audio experts don’t guess better than chance would dictate.
Depends upon your library.
If growth of filesize exceeds your storage growth, you're gonna be screwed eventually.
I have about 17,000 tunes on my computer. They are all pretty much the highest quality mp3s that I could create from CDs. The difference in quality will largely be lost on fogies like myself who's hearing has been impacted by stupid volume levels when I was younger, and firearms as I aged. Given the situations in which I mostly listen to music. i.e., sitting at my desk while working, and in the car/on my bike, sound quality isn't nearly as important as breadth of the library. I love the fact that I can be listening, and hear a track by Maroon 5, followed by a Bach Sonata. Keeps my day interesting.
I keep the CDs around so I have a master that I can use to replicate my data any time I want. I still have the very first CD I ever bought. (DSOTM) I really love the fact that it still works after all these years. I'll never have to re-buy my library as was inevitable with vinyl, even with the most careful practices. It is this that I love best about the new digital world. If I someday decide to buy some disks of this new encoding type you are describing, changes are it will be new stuff, and not things that I already own.