Here is why I don't want Manning.
He has zero management experience. Being a great footballer won't make him a great GM or whatever position you want him in. You want people who can identify talent an get rid of deadwood. The way Miami is, you need an experienced GM.
Tannebaum needs too go, no doubt about that, and go now. Start looking for a replacement who knows the football front office. Who knows how too draft and trade.
Manning has no experience in that.
I'd take a zero experience Manning over a tenured Tannenbaum every day of the week. Manning would learn on the job and be just fine. In 2 years he would be more proficient in his duties than Tannenbaum would in 2 lifetimes.
I don't know who will be available when Ross finally throws his arms up and says 'enough!', but I doubt I would trust any of them over Manning.