You may be able to remove Windows ability to allocate the IRQ's.
Try going into the motherboard BIOS and telling the BIOS to take control of the IRQ allocation. Sometimes, the BIOS makes a better job of it than Windows.
Having one IRQ sharing four components is almost guaranteed to slow something down and in this case, it's your sound feed.
Frankly, I don't know if it will work, but it's worth a try.