Why not post your website here, let's see how come you made only that much money and you got so much traffic. Can you share how you get so much traffic?
You can make more cash. 20k visitors on daily basis is good and why not consider something new? I believe you can't place google ads due to...and you should add more content. 57k page view and 20k visitors per day mean each visitor only view 3 pages.
Adbrite is paying much less than adsense, but of course adsense is not an option for you. In my opinion you have three options : 1) Use pop up programs 2) Play with the ad placements/colors 3) Do both