As for Marchenko I am pretty sure you need to send the player down prior to the trade deadline for him to be eligible for the AHL playoffs. (silly rule) I did not see that he went down. I do not know if there is an exception if the player is on IR.
You can't send a player down while he's on IR. They said they would send him down when he's healthy. They sent Jurco down (only on paper) to make him eligible for the AHL playoffs. They had to do that because Jurco hasn't played in the AHL this year, but the paper transaction I guess makes him technically an AHL player. They wouldn't have to do that for Marchenko since he's played substantial time with the Griffins. I think he'll be sent down to keep him playing. There's no sense in keeping him as the #7 and allowing his game to get rusty.