Help with PCM, 96khz/24bit, 176.4khz/24bit FLAC, DSD, Double DSD, Quad DSD, MQA, WAV, etc

It is easier if you separate the terms. It's really not too terribly complex.

PCM & DSD are the two fundamentally different digital philosophies, and within both, you have different resolutions.

PCM 
16 bit 44khz is CD quality
24/88
24/96
24/176
24/192
these are all increasing resolutions in the sampling.

DSD, double, and quad DSD are a similar representation of higher resolutions in the DSD path.

so that is the way that the digital music is created in its analog to digital conversion from the master tapes as it were.  Now we have to save the file and choose a format of the file itself.

WAV - windows based, fully uncompressed file.
AIFF - mac based, fully uncompressed file.
FLAC - windows based, lossless compression
ALAC - mac based, lossless compression
MQA - newest kid on the block, promises lossless compression but delivers a smaller file size compared to FLAC and ALAC.  After the file's oragami is unfolded, you can get a high res PCM file.

so, what should you buy? Depends on your gear.  I have a dac that can handle 24/192 PCM. It cannot handle DSD.  If I buy high res files for use today, I would buy 24/96 or higher. If I buy for the future, I can buy DSD and my software (Roon) can translate the DSD file to a PCM format that my DAC can handle.

As for MQA, I am streaming those from Tidal, and my Dac is unfolding them and they yield a high res file.

hope this helps!

The encoding is different from the file type.  So FLAC, ALAC, WAV, AIFF, etc are all file types that a music file can be saved as.  This is independent of the resolution and bit depth.  The file types I mentioned above are ubiquitous, and most all audio players and DACs support these file types.  Furthermore, there are audio file translator applications that can take a FLAC file and make it into a WAV file, etc.

Before I get slammed by the community, let me say that what I posted in the first answer to the OP is a simplification of the terms and concepts in digital.  I am sure someone can find something not quite right about my response, but more or less, it is accurate.

As for the difference between the (lossless) compressed file types of ALAC and FLAC versus the uncompressed file types of WAV and AIFF, a lot has been debated on this.  I listened and could not discern a difference.  I chose AIFF in the end for my music collection for more theoretical reasons.  In order to compress a file, with or without quality loss, the original file needs to undergo compression by means of a compression algorithm that finds way to make the file size smaller.  When the music will be played, this compression needs to get undone in reverse.  My way of thinking is, storage is cheap and plentiful, I would just rather that the files avoid this extra step.  In short, I just don't require the space saving of the FLAC and ALAC.  I chose AIFF as I am a mac user, and this is the native mac uncompressed audio file format.

As for the sound of the Tidal MQA files, I have not listened closely enough yet.  I have a Tidal HIFI membership, and I use Roon to stream the music to my PS Audio DAC.  Roon and PS Audio do not yet have a full MQA unfolding implementation.  I can bypass Roon for now and get the MQA unfolding with my DAC, but I like Roon, and the regular CD resolution files from Tidal sound great on my DAC.  Once Roon offers an update, I will be happy to listen to more of the Tidal masters!
Hgeifman, don't worry what file type you purchase for now.  FLAC is fine.  You can try another later if you like, but for all that I can tell, lossless is lossless, and the files are good.

Have fun!

We think alike :-)
I trust DSD is great, but so is high res PCM. 
I listen to 70% vinyl, so until I upgrade to a DSD DAC, perhaps in a few years, I am happy with any files that are CD quality or better.