Like a lot of audio there are diminishing returns. Your USB connection sounds like it always did, but there seems to be a consensus that Ethernet to a network device with USB to the DAC can be an improvement.
A USB connection has a 5v line and an earth. Computers are a notoriously noisy environment and that noise can propagate into a DAC via those lines. There are various techniques for minimizing such noise including software optimization, improved power supplies or separate power supplies/batteries for various components. Some people cut or mask the 5v line but the earth line must stay open and it provides a galvanic connection into the DAC. These tweaks and optimisations can get as expensive as you like.
Alternatively, you can send the data by Ethernet to a small footprint network device and then to your DAC, usually by USB. This enables you to create a dirty side and a clean side for audio purposes. Provided the Ethernet connection can fill the buffer on the network device it doesn’t matter how noisy or jitter ridden the output of the dirty side is. You can then concentrate on keeping the network device “clean” rather than the Augean stables of a general computer.
There are some qualifications to this architecture. Although Ethernet has small transformers at each end which reduce propagation of noise they are not as effective as fibre, which absolutely ends any galvanic connection. There can also be a noise path through shielded Ethernet cables, some computers (Apple in particular) have little studs next to the Ethernet port which connect shields to an internal earth.
There are also reports of different sounding Ethernet cables, but no consensus about this. I’m agnostic as to this possibility. The effect is not reported to be substantial.
So, in short, choosing a quiet network device and feeding it clean power is generally accepted as providing better bang for buck than tweaking the computer.
There is a page in the KB about this, I’ll link it when I’m off my phone and back on a desktop.