They are all bigs except DW, but then if we keep Rondo there's no need for DW. So my preference is here:
Kevin Love
LaMarcus Aldridge
Marc Gasol
Melo
DeMarcus Cousins
Al Horford
David Lee
Brook Lopez
First off, I appreciate the work you did putting this post together. When I first read the title, my response was "any team could be a legit contender if you added 2 all NBA players", but after reading your post I commend you for putting this together.
Now, here's my opinion on your list.
I would love to get Kevin Love and/or LeMarcus Aldridge, but I'm not sure why Minnesota or Portland would trade them. I don't believe Rondo and Melo would be a good pairing because they both need the ball in their hands a lot. When the Kings traded for Rudy Gay it showed me that they want to win now, so it wouldn't make sense for them to trade Cousins unless it was for Rondo and I think that would be counter-productive for us. Brook Lopez is out for the year. And, for me, given the choice I would rather have Sullinger starting at PF than David Lee.
That brings the list to:
Marc Gasol
And
Al Horford
I would add either of them in a heart beat if the price was right. I don't, however, think I'd want to add both. It would take our naturally up tempo team and slow us down. Adding one of these guys wouldn't immediately make us a contender, but would help a lot more than Asik would.
I would also like to keep an eye on New Orleans. They have a bunch of talented youngish guys and they may not be able to keep them all long term, so they could cash in now. So if we were to add either Gasol or Horford(or Love or Aldridge if Danny can pull off a miracle) it might make sense to trade for Eric Gordon or Tyreke Evans.
To Rondo and whatever assets we don't trade, we'd be adding a talented Big and a scoring wing. Could be something interesting. Or we could roll with what we've got and see what the picks become.
Anyways, just my thoughts on your proposal.