Just to add more info to this thread, I recently purchased a CPO 2022 MDX Advance to add to my 2013 TL Advance.
After much testing, I have determined that my 256G Samsung Fit Plus USB stick can be formatted FAT32 or exFAT, either way it works fine. I've got that baby packed with tons of 5.1 FLAC, stereo FLAC, WAV, and MP3 files, and they all work fine. For people who ask where they can get 5.1 test files, this page has the files from the old Acura DVD-A's.
https://drive.google.com/drive/folders/155gEwxEWzrEccXoovC4UEFixpXzxqXbl
I have all my albums in directories which are seen by the ELS system and listed alphabetically. You can organize directories in sub directories as long as you don't go over the file name limit. The ELS will read the metadata (except on the WAV files of course), and it sees the album artwork, the artist, and the song name, but it will not see the track numbers not matter what I do.
I had to go back and spend many hours prepending a 01, 02, etc to the beginning of each song title in the metadata using MP3Tag for the songs to be listed and played in the correct order. Otherwise it lists and plays them alphabetically. What a pain.
To be upfront, there's no way I'm ripping all my DVD-A and DTS CD's to FLAC, I don't have the time or an optical drive to do it. Just about everything I want is on Usenet so I signed up for Newshosting to download everything. I try to find 5.1 FLAC versions of my music, and if not available, I try to get DTS 5.1 versions. I use VLC Media Player to convert the DTS files to 5.1 FLAC because it's very easy and fast. An entire album takes a couple of minutes to convert. I only use MP3's as a last resort, and I'm going to get rid of any WAV files since they can't have metadata and they're huge.
Obviously 5.1 FLAC files sound the best on the ELS compared to any of the stereo versions. To be honest though, playing DVD-A in my 2013 TL sounds a lot better than anything I throw at the MDX, even with 6 less speakers. I think it's the smaller cabin size, since even an RDX sounds better than my MDX. The TL can hit you with a visceral punch from every direction with no distortion, while the MDX is front biased and starts to distort at about 50% volume. I'm definitely going to look into replacing some of the rear speakers to compensate.
And for those wondering, I tested 2025 MDX's with the B&O systems (an A-Spec and a Type-S) and they both failed my 5.1 tests. They're stereo only which is a disappointment, although the systems do sound good. One weird thing is they absolutely will not read a USB-A stick using any type of USB-C converter, I had to buy a USB-C stick to get them to work properly. For us ELS lovers, I think this is the end of the road once they convert all the other models to B&O, although listening to the newer ELS systems, I don't think Elliot Scheiner is really involved anymore since the quality has gone down. Just my opinion.