What am I doing wrong?

Thanks Mlsstl, I use my phone at present which has a dedicated Bluetooth processor, the trouble is that the Battery, Clock, Processor go out of Sync, which causes high pitched change to the audio, tried changing to the processor generally used in the phone, that is no better.

Then maybe consider a DAP?  I think some of them support external drives but you'd need to check the specs carefully. I have a Hiby M300 which I like but it only supports micro SD cards, though you can upload additional tracks to the card using the USB C input.  Lots of DAPs on the market so I suspect you can find something that will work for you. 

Any streamer etc with a USB input should work with the correct adaptor. granted the streamer etc can use external storage devices. 

Aah, I don't trust the Astell & Kern type devices, because they are so much like a phone. So it looks as though I am drawing a blank presently. I looked at streamers and they are Amp/Headphone/ Wi-Fi Heaven, just not mine

Interesting that you are currently using your phone but indicate it causes "high pitched change" to the sound quality.  But then you say you don't want to use a DAP because it looks too much like a phone. 

One other thought -- you could try a Raspberry Pi with the Raspberry Pi or pCP OS and enable the LMS (server) program. This would allow you to plug in external storage devices (USB A inputs) which could be managed with a browser program on your PC, laptop, tablet or phone. You'd still need an adaptor for SD cards. And you'd probably also need a bluetooth dongle for that feature.  You'd need to do some research to make sure it does everything you want and then more setup work than for a preconfigured device, but you could customize it as much as you want.  

If that doesn't work for you then I'm out of ideas. Not sure there is anything out there that does what you want out of the box other than a DAP device which you've indicated you don't like for cosmetic reasons. 

Good luck!