Where is my bottleneck?

[91tyler]

An easy alternative would be to move music listening to a fanless device like a tablet or a Raspberry Pi-based miniPC.

Ok that I understand haha

 

[galveston22]

The blue jeans cable

 

[czuba]

An easy alternative would be to move music listening to a fanless device like a tablet or a Raspberry Pi-based miniPC.

This was going to be my suggestion, as well! There are various solutions adjacent to this, as well.
In fact, it was already more-or-less suggested above by MonsterZero, who mentioned an Intel NUC. Asus makes the Tinker Board. You could also buy another older machine and turn it into a home media server. If the desire is to use it just for headphones, though, you'll probably do best to run the simplest system possible. That would be a single board with added storage. The main challenges here will be configuration of the OS and choice/configuration of related software.

 

[ProtegeManiac]

This was going to be my suggestion, as well! There are various solutions adjacent to this, as well.
In fact, it was already more-or-less suggested above by MonsterZero, who mentioned an Intel NUC. Asus makes the Tinker Board. You could also buy another older machine and turn it into a home media server. If the desire is to use it just for headphones, though, you'll probably do best to run the simplest system possible. That would be a single board with added storage. The main challenges here will be configuration of the OS and choice/configuration of related software.

Plus the control and screen if instead of a monitor via cable (there's already a computer on the desk, you want it on a smaller nightstand, etc) and a mouse you want to set it up to be controlled by a tablet or smartphone.

 

[czuba]

Plus the control and screen if instead of a monitor via cable (there's already a computer on the desk, you want it on a smaller nightstand, etc) and a mouse you want to set it up to be controlled by a tablet or smartphone.

Haha, those details were intentionally (slyly) embedded in "main challenges here will be configuration of the OS [...]". Configuring these boards take some technical know-how, especially if you want to run it headless -- but this is arguably the best solution. There are plenty of FOSS applications which can be used to control the music from a smartphone or elsewhere, all with excellent options for downsampling, if desired, for more casual wireless play around the house. Though some will argue that adding that extra functionality will add "noise" to the "blackness" of your signal -- I'm more partial to the opinion that this is irrelevant prior to D/A conversion because binary encoding is, well, binary.