Just to add to these posts, I 'd though I'd also post the roster rules:
(D) BUYOUT OF GUARANTEED CONTRACT
A club may buy out one player who has a Guaranteed Contract (including a DP’s) during the offseason and free up the corresponding budget space. Such a buyout is at the MLS club’s expense.
A club may not free up room in the salary budget with a buyout of a player’s contract during the season. In the case a team buys out a player’s contract during the season, the buyout amount will be charged against the club’s salary budget.