I agree, in my view, it would take a DAC many times its price to better the T+A.
For every DAC to interface with Windows it requires a driver. This is a difference in how operating systems work. I do not claim to be an Apple expert (to say the least), but one of the big differences between Microsoft and Apple has always been that Windows is an open system while iOS is a closed system.
What I mean by this is that Windows has always been able to use almost any hardware that become available. It requires a driver (a software program that allows for interface with the new hardware), while Apple has always tried to bake in the interface with new hardware and do not usually use drivers. Therefore they can, and do, control any and all hardware that can be used with iOS. A DAC operates in the exact same way.
iOS has baked in a standard DAC interface up to DSD128 using DoP, but anything above that has traditionally required native support, and drivers. Unless this has changed this is how it works and why the T+A requires a Windows computer.
I have never used Linux. However my understanding is that Linux is the wild frontier, so to speak, and anything can happen. It is more for the DIY crowd and should be able to be modified for whatever the user wants, so long as they have the know how.
Many server builders use Linux because it is free and they can modify it how they want. However most are not willing to develop software to interface with any DAC out there so they stay more with the standards which are about the same as Apple uses. Also, there are so many variations and customization's in use for Linux that most hardware manufactures would be unwilling to attempt to create an interface for their hardware since it would not work with many or maybe even a majority of the Linux installations in use.
Again, this is my understanding but I make no claim that this is how it currently works, however this is definitely how it used to work.