SACDs are something else, and these discs require a special player to play. You cannot rip a SACD using a standard PC CD-ROM drive (or DVD drive or whatever). I believe most people use a Playstation rigged up to their computers somehow to do this?
Older versions of the PS3 had SACD playback support and allowed you to set up "Other OS" (Linux) on them.
If I recall correctly, an exploit was found in the hypervisor, which allows people to install and run homebrew "apps" on the PS3.
Someone has written a tool for this which will dump an SACD disc to a connected thumb drive, or allow you to rip it over a network connection using a command line tool on your PC.
However Sony have removed the "Other OS" support from newer firmwares, because it was mainly being used to pirate PS3 games, and newer models of the PS3 hardware no longer have drives with SACD support.
So you need to find an old model PS3 which is still working and has not been updated beyond a certain firmware to do this.
It's quite a hassle, but there's no other way to back up your SACD discs, or have the convenience of using digital files instead of physical media.
Some SACDs are hybrid discs and you can rip the CD layer from them though.
I've never heard of K2HD, so I can't help you with that.
K2HD are just
really well mastered CDs. I imported a handful of them from Japan and they all sound wonderful.
But they're still redbook spec 16/44 PCM audio.
But, the basic deal is: If the disc will play on a regular-old CD player, like the ones you'd have in a PC or in an AV Rack, and doesn't require a specialized player, then it is a redbook audio CD, and is 44.1kHz PCM. And, if so, then what I said above applies: FLAC, APE, WAV, and AIFF will all produce identical results (also ALAC, I forgot that one).
Exactly. Anything that you would call a "CD" is 16/44 PCM audio and should be ripped to one of the PCM encoders. There's very little reason to use the DSD encoder at all - you would have a specific use-case for it and would know exactly why you wanted to use it if you did.
If you have any HDCDs, you can rip them just as you would with any normal CD to 16/44 PCM files.
But you can then run those files through a HDCD decoder (I use dBpoweramp's tool) which will extract the 20-bit audio and put it into a 24-bit container file.