In TCP OPtimizer It is possible to enable TCP chimney offload as well as NetDMA. That is clearly wrong, since both are mutually exclusive. If TCP Optimizer finds both enabled, it should give a warning.
I disabled NetDMA, and enabled TCP chimney offload. The Realtek NIC already had all the appropriate settings, all 'offload' settings enabled. Despite all that, when I issued 'netstat -t' I saw everything was handled 'Inhost', so the TCP chimney offload doesn't work. You should always check if the TCP chimney offload is working, there are many reasons why it will not work. So I disabled the TCP chimney offload, and enabled the NetDMA.
What the Direct Cache Access is actually doing is a mystery to me. I can't find any documentation at Microsoft about this setting. Is it also mutually exclusive with other settings? Who knows.