My DS58SO board has been very difficult for me to debug. This is the 3rd board I received, the first board was missing the audio power plug on the board, the second one had this networking issue, and the 3rd had the same networking issue. I found it is a driver problem because I purchased and installed Windows XP 64 bit, installed it, and had no problem at all.
I have a Trendnet TEG-S80g gigabit switch, and Dlink DNS-323 fileserver. In Windows 7 64bit, the DX58SO can download from the fileserver at approx 18meg/second, but uploads back to the fileserver at 175 to 235k/second. Network connectivity was not stable, downloading software updates would fail, and i'd get kicked off of World of Warcraft after a few seconds. I have the latest 10.1.6.0 ProWinx64 drivers installed, and the tests say i'm running a cable that exceeds 100 meters in length, but my CAT-6 cable is only 12 feet from the gigabit switch.
So then I purchased a copy of Windows XP 64bit, installed that, and everything was fine. Files would send and receive at approx the same speed. Network connectivity was very stable. I purchased a Trendnet gigabit ethernet adapter, installed it, replaced the Windows 7 64bit, and everything is fine. So i'm fairly certain the problem is with the Windows 7 ProWinx64 drivers.
I would rather use the onboard ethernet adapter so thought I would post this. Hope this gets to the support teams that deal with those drivers.