How do I rip 5.1 surround sound DVD-audio into a playable format for Sonos?

I’ll start with the problem I’m having in as few words as possible:

I have “remastered with 5.1 surround sound” remixes of classic CDs, packaged as a bonus DVD on a CD box set.  (Many of these...so many I’m wanting to remove the need for physical discs and rip them to my NAS so they can be played quickly and easily).  Sonos WILL play them when I rip the DVDs as .iso files.  But those files are huge and the system bogs down and I don’t need all the DVD content, only the DVD audio 5.1 material.

Now the problem.  No matter what I try, and I’ve tried everything, either Sonos doesn’t see the folders containing the files, OR it does see them but complains about them being unsupported.

I understand Sonos supports 24 bit and 48000 kHz.  So I encode with those settings but it still doesn’t see the files, or doesn’t like them.

There must be some combination that works.  They absolutely need to be multichannel for the surround sound to work.  And if THAT is the problem, why does Sonos have no problem doing that when I play the .iso file of the DVD?

.WAV files are much bigger and less desirable but I’d do those if I had to.  But even with all the metadata loaded into them, Sonos doesn’t even see the folders.

I spent a lot of money on these deluxe box sets to hear them in surround sound, can someone assist me so that I can hear them without a bunch of disc swapping?