On one computer (a P4 with SB128) I had to set Plug&Play to OFF so that the system BIOS would configure all PCI devices.
Now, on this P4 machine, I can see a potential problem you might have.
On the p4 machine I installed many audio codecs.
Some of the codecs don't seem to work well with the driver.
Are you only having trouble with certain compressed wave files and audio codecs?
I tested an AMD M5A78L-M/USB3 with a third SB128 and the USB mouse did not seem to cause breaks in the audio.
Since I don't have a PCI Voodoo video card and I don't have your particular Network setup, all I can do is guess.
On these machines, MP3 and MOD files are working just fine.
Do MP3 files still skip when you disable your network drivers? (win/N)
The DOS USB drivers require an intel compatible UHCI controller.
For the exact details of how the DOS USB drivers work, you might want to see the authors web site.
Were you testing 123USB05 or USBAUD2?
The 123USB05 driver is the latest version.
Are you trying to use more than card at once or more than one of my drivers at once
Although USB123 should work in parallel with others, the HDA and 137x drivers might not.
16th June 2020
I've found that the AMD FX motherboard has some issues with my USB keyboard and mouse.
At first everything works well, however, after a while both the mouse and keyboard start acting goofy.
It looks as though USB devices are not being handled properly by the BIOS.
Does this problem sound similar to yours?
20th June 2020
I tested MP3 files on my 550mhz Pentium III using Windows 3.11 and yet another ENS1373.
It would seem that music playback was uninterrupted.
My Pentium II 350mhz with 137x also plays just fine.
I tested crea1371.dll and Winplay3 on a 133mhz Pentium MMX.
Even at 133mhz, MP3 files seem to play without skipping.
Big Monstro, when do the problems in mp3 playback occur?