i got a similar problem with my board.
if you do a DPC latency test, disable you realtek lan controller, big chance you dont have high latency´s anymore.
I got the same problem, the dpc latency tester, i checked my sound latency, i play a song in winamp and after 2 minutes i got an error, the log file of dpc tester, told me that is was probably cost by the realtek lan chip. So i disabled the realtek lanchip in device manager, and dit the test again, for 15 minutes wit no errors at all. no latency peaks over 1000 anymore, But as soon as i enabled the lan chip again, bang, error.
Since your Sabertooth and Gigabyte both use the same realtek lan chip, its most likely caused by that.
What you could try, if you have a pci-e lan card laying arround (not from Realtek) to install that one. And look if you still have those issues.
I also tried everything to solve it, i tried diffrent drivers, bios updates, reinstalls everything nothing seems to solve this. I only did not tried a diffrent nic, because i dont have one laying arround.
You could also try to disable "all sound effects" on your playback devices, for some people this solve the problem with high cpu ussage audiodg.exe. But in my case this is not a good solution, cause wenn i disable it, the sounds in my online flash and java games does not work anymore.
I think that i´m going to replace my mobo aswell, but the with the Asus crosshair V Formula Z or Asrock Extreme 9, cause these boards have an intel lanchip. But this still does not guarantee me anything.
It seems like an Windows 7 issue in the first place.
I feel your pain lol, cause im getting sick and tired of it. Before im going to replace my motherboard, i will install windows 8.1 on a diffrent hard drive, just to look if thats maybe the issue.
Read this topic about it, there are more people with the same missery in Windows 7.
Grtz Angel ☺