If the concern is that there are too many people on stage, then we should narrow the focus of the debates to one issue at a time with longer answers by each candidate. So we could have a debate on the Iraq War, give each candidate two minutes to have their say, followed by fifteen minutes of open rebuttal time facilitated by the moderator (with a light touch, avoiding egoistic grandstanding--yes I'm talking to you Wolf Blitzer), and ending with two minutes for each candidate to conclude after open rebuttal. That's 47 minutes, which is only slightly more than a typical broadcast hour with commercials, which could be sandwiched between the three different stages.

Then have a completely separate debate entirely on health care with a similar format. Have another one on constitutional and civil rights. And so on. That's how you get more in-depth answers despite having eight guys on stage, without arbitrarily excluding any candidates.