As tough as it is for me to say, I'd want to keep AP, and roll with Big Ben. The Steelers will still be throwing a lot, and AP is a beast in non ppr leagues.
I would not do this deal "as-is" as I don't think you are getting anything close to value for AP. You have the best 1-2 combo at RB in the league... so you are able to dictate terms a little more.
I think in order to make this deal work, I would swap out Knox for a top-10 WR.... then I would consider it.