I have a question about Adsense as I know little about them: can Adsense ads be displayed with other ads (ie: sponsors ads)? I'm asking to determine how I will integrate them.
Adsense ads are just a code that churns out google ads. What you are looking for is the management.
You can implement Openx into it to control global/zone inventories of advertisements. You can even base them on location, time, size, campaign, advertiser, forum, thread etc. It's a simple code just like the google adcode to specify whats what.
I figure you are elaborating on 40% Adsense, 20% Yahoo ads, 40% random ad agency; that is doable. Google Ads at 2pm-5pm EST for only people in New York during every other friday of the month up until it reaches 1,000 views while only showing for new visitors at their first 3 visits is also doable.
You have the admin account, others log in as users where they can control their zone's inventory. You operate, own, and manage the entire service.
I'm pretty sure you can force 30% of the ads being ran to in-house while leaving the other 70% configurable to whatever the site owners want. But don't quote me on that because I haven't tried it.
We use it in our 728x90 adblock which is integrated into vbulletin on
http://www.fohguild.org/forums so it shouldn't be too bad on Xenforo