These are another option - remote USB over a network, wired or wireless.
**broken link removed**
I did test one with a USB sound card module a year or so ago and it worked fine.
Re. multiple USB sound devices, note that some makers do not bother with proper unique IDs in USB devices that they only expect to be used singly and the drivers cannot handle multiple instances.
I'd suggest just trying two together to see if they work before buying many.
Also consider audio interfaces intended for music production if you need a lot of audio channels.
You can get those with many input and output channels and exceptionally high quality compared to PC sound card audio.
The USB3 Presonus studio 192 unit I have has 26 audio inputs and 32 outputs.
[You can also get direct ethernet connected audio interfaces, though they are still in the early days and expensive!]