I was able to work it like this:
We're left with 1.85 million to sign two 4th line forwards. That's including carrying Domingue and Petrovic as a 3rd G and 7th D. Given the FA/PTO market has some interesting players that will require very little on short term contracts I think this is easily achievable. The situation actually improves if we keep Hanifin but I think that's part of the benefit for Buffalo. I break the trade down like this:
Mangiapane < Reinhart
Hanifin > Ristolainen
Rittich >= Ullmark