OP - you will want to use an open source ad serving platform in order to display ads including adsense as well as ads from other people. Generally these would be in a rotation. You still don't want to show more than 3 adblocks on the same page because it will drop your overall quality scores, and bring your earnings per ad click down. So just use the top converting 3 slots, and then setup an ad rotator so that you earn revenue from your multiple earnings opportunities. So you would put your adsense blocks, chitika, etc... in the rotation and it would serve those ads based on the schedule your tell it to use.
I hope I understood your question well enough. If you really want to show more than 3 ads per page served you can do so, but it will significantly reduce your click through rate as well as your earnings per click. Good luck!