Depends on your formation though mate. If you're playing a 'flat' 4-4-2 then you're spot on - although with the mentality changes you're actually going to be playing something more like a 4-1-2-1-2 as the MCd drops deeper into the DMC position and the MCa pushes up into the AMC position. That's basically the 4-4-2 as a diamond but without needing a DMC or an AMC.
Sacchi and Benitez actually use/d two playmakers as standard with a third for breaking down tight defences. So Baresi, Rijkaard and Gullit for AC Milan or Agger, Alonso and Gerrard for Liverpool. Using a defender as a playmaker is something which is normally standard for the old 'libero' sweeper systems where the sweeper brings the ball out of defence into midfield, but you can see this idea being used elsewhere too - Paisley liked one of his central defenders to be able to carry the ball out of defence and you can find other examples before 'Sacchi'. Matthaus (spelling? German midfielder who was fantastic) became a sweeper in the Beckenbauer style when he no longer had the pace to run the game from midfield. He led Germany and Bayern Munich to some success doing it.
So a 'playmaker' doesn't really need to be a central midfielder - in fact, the idea and naming of player as a 'playmaker' comes from the idea of playing a skillful player behind the front striker. So Cantona or Yorke or Sheringham for the Mancs under Ferguson in a 4-4-1-1 system - or you could have Dalglish or Beardsley for Liverpool in the late 80s, or Gullit for Milan playing behind Van Basten. Hence the player in the AMC position with freedom to move about - as you see with Gerrard at Liverpool right now.
The downside to playing in the AMC position in the English league is that teams have figured out that they can't allow the opposition that much space (Cantona and Zola made careers in England exploiting the space left in front of defences when the box-to-box midfielder of the opposition couldn't get back in time to cover). Clough was the first manager I recall in the English game using a playmaking DMC - a player like Neil Webb was used to run the game from in front of the defence, Liverpool also had a similar type player in Jan Molby. If you play a player like this then the opposition have a problem in how to close him down - the strikers will not be near him usually and pushing up the midfield means there's a lot of space to exploit behind them unless they are packing their midfield and have a DMC. Hence the 'defensive' 4-1-4-1 formation which kind of solves the problem in controlling space but does limit attacking opportunities without someone capable of playing up front on their own.
That's why 4-2-3-1 has now become so popular amongst very top teams. You can have a playmaker deep partnered with a DMC to nullify the oppositions playmaker, whilst also having a playmaker behind your worldclass striker. In terms of covering all the angles, it does the job. You'll see the AI managers in 09 using it when you have a good 4-4-2 tactic because it does shore up the defence while offering problems to a 4-4-2 defensively by occupying the fullbacks, demanding that the MCd stays deep etc. If you add in a player capable of stepping up from the defence into the space left by the opposition trying to cover all the offensive options, then you get a formation which is balanced in both attack and defence. Until someone then comes along with a formation which nullifies it (the W-M formation is superb at this - it's a formation which English clubs played 50 years ago!).
So my point really is what works well for one game against one formation may not do the same in another game against another formation. FM tries to emulate real life and does it well at times. What's needed from the player of this game is the ability to say "Plan A isn't working, let's try plan B' and knowing how to change things around. So if you're playing a flat 4-4-2 and getting nowhere on that particular day, how about pulling the MCd to a DMC and pushing the MCa to an AMC? Or pulling the FCd back to an AMC position..