Moneual MonCaso 932.
Fair warning, a $50 Android tablet won’t be very enjoyable. Will probably have poor resolution and responsiveness.
I’ve been using Sonosfor almost 10 years. Music ripped to a NAS and feeding various Sonos units ranging from the self-contained Play series, a Connect:Amp driving Martin Logan wall-mounts, to various Connects driving everything from a whole house PA amp to a $50K Meridian system. All controlled from tablet or smart phone.
Found what I was looking for!
Drum roll…
Logitech Squeezebox Touch
Will take a USB thumb drive or a SD card. Designed to sit on a shelf in your living room, no batteries - plug-in. Connects to your stereo via optical, RCA L/R, or headphone jack. Comes with a “TV style” remote control.
And the large screen so you can see your folders/songs listed!
Here is a CNET review…
According to the linked story, this product was discontinued in 2012.
Virtually any media player can send it’s output to your stereo through an analog cable.
Your OP is full of confusing stuff. No stereo on the world that I know of “knows” what category of music any given track should be in. The user defines what the categories of music are, and assigns the tracks to one or more of those categories.
Most people do this on a computer and then load some or all of their music from it into a portable media player, or run a cable out from their computer into their stereo to play the music that way.
I can’t figure out why this is not good enough for you. You seem to want a giant media player that can do what a computer can do, and have a really large screen (just like a computer does, go figure), and have an amp that powers the speakers directly.
Why do all the parts have to be in one box?
A few appear to be available on Amazon.
OMG, $700 for a new one? $350 used? Thanks, I’ll just use a tablet.
Ebay has them too.
I found another player which was RIGHT UNDER MY NOSE!
That is my old cell phone! I was tinkering with the SD card in the Logitech Squeezebox Touch and got to thinking what size SD card was in my old, no longer used, Android cell phone?
Bingo! There is my tablet! I searched on the internet and found I can set the old phone to Airplane Mode, Wi-Fi on, then can download apps via Google Play! (Then use Rocket Player which will easily access folders on the SD card.)
Well I did this, bought a 16GB SD card for it, copied my music into the Music folder on the SD card, and now have a second “CD player”. I can connect this to a second home stereo I have in my house.
As for which I prefer more, Squeezebox or Android Cell Phone-Rocket Player?
The Squeezebox does not have any batteries -designed to be plugged in like a stereo component, but it keeps wanting to connect to the internet. Does not like having power totally turned off.
The Android cell phone also needs to be turned on/booted and has a battery which will need to be replaced periodically, but the rocket player app is MUCH easier to operate so far as switching to different folders/favorite music. Also used cell phones are much cheaper if you have one laying around!
OK, the Squeezebox Touch is a POS!
It will only index a maximum of 100 songs. And when turning it on from total power off, it wants to connect to the internet. A pain if you just want to play songs from the SD card or a USB thumb drive.
So I am going with older Android Cell Phones which you can get on EBay for $20. And then just copy the music to the SD card (install a 16 GB SD card). Cheaper than a tablet and the Rocket Player app makes it easy to play songs from a particular folder.
For example I don’t want Christmas music to play year round. I want to switch to that folder and play it at Christmas time. And maybe sometimes play Disney type music for small children. Want to be able to switch to that folder and play just that.
So Android tablet or older Cell Phone in airplane mode (cheaper) is the way to go!
Just wish something had these features without the battery. More like a plug-in CD player. Or the Squeezebox where you could turn off the internet and just play what is in various folders - not need to index everything.
That’s what playlists are for.
100 song maximum?
You are actually making this way more complicated than it needs to be, primarily due to your requirement for on-board storage.
All of my music is on my PC, where I also have Plex installed. I have the Plex app on both my phone, and my tablet. I can stream to any blue-tooth enable speakers, or to a blue-tooth receiver connected to my stereo. Heck, I can even stream it to my car.
I can make all the playlists I want, with no song number limits. And, I don’t have to fuss around with thumb drives or SD cards.
No, I am making it simple!
I get in either of my cars - without a cell phone, I start my car, and the music starts playing. (From USB thumb drives.)
Simple!
I walk in my living room, turn on the main power to the stereo, turn on the cell phone, and turn on rocket player - music starts playing. Plus I have easy access right there to different folders - no internet or PC needed!
Simple!
Same with my rec room - it will be the same cell phone setup with rocket player.
Simple! Plus I am saving on electricity because this stuff is off when not in use.
And best of all, no monthly fees, no irritating Microsoft update screens.
Not on any tablet or phone.
Right! One of the reasons I decided a tablet/phone was the best route to go.
Well of course it’s a good idea, it’s what I suggested like two months ago. 
My point was that you shouldn’t be using folders to organizer your music on your phone/tablet, you should be using playlists.
Well I have two different car stereos which play by folders - (no play lists). And 3 cell phones.
On my computer I have copied the various songs into appropriate folders. This works on ALL my devices.
Simply select my favorite songs ONCE, then copy the folders to the various devices/thumb drives/SD cards.
And play music by selecting the folder I want. Copy/paste is all I have to do to set up all my favorites on all devices!