Eric, a 20DA is surely a step backwards from the modded 350 - less Ha sensitivity, likewise the 40D (but you get better usability features and lower noise). I can only think you must go to a cooled system of some sort to get better results, I think narrow band is the other way maybe the DSI III + filters I do not know the beast but if your budget is tight how about those QHY cameras....
http://qhyccd.com/QHY8.html
BTW if the modded 350 sale falls through let me know - after trying to image ic2944 I have seen the light - or lack of it - now I want a modded camera. Currently hanging out for the 450...