What am I doing wrong?

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! 

Thank you for your help, the Raspberry pi Option is an interesting one and I will look at that with pleasure.

My reservations about a DAP simply stem from my belief in it's capability to monitor itself. I think it will be likewise a phone with the inherent battery problems and therefore with a clock misalignment. Not noticeable with headphones, but with large speakers.

As respects a DAP, perhaps order one from an online retailer with a full money-back return policy.  If it works, problem solved! If it doesn't send it back for a refund.