HDAMA motherboards come from Arima, http://www.rioworks.com/HDAMA.htm They are supposed to have two Broadcom 5702 gigabit Ethernet chips in them, but may incorrectly have the 5705. The 5705 does not support jumbo frames. Check the board itself and if you have the wrong chip, you can contact your vendor for an RMA. (I don't know if the HDAMB is similarly affected.)
