The HDW 1800 has a downconvertor to SDI. I presume you are actually capturing HD footage, but wanting the SD downconvert, or do you have an HDCam that plays digi beta?
Either way, the SDI outputs to Kona SDI inputs are the best way to capture. Also the issue may be the field dominance setings. Check the menu in the HDW1800 to make sure your field dominance output matches your capture settings. In PAL this is easy because it is all upper, but NTSC might be swapping dominance from HD to SD