I can see how it is possible to undertake the JAA MEP rating in 6 hours plus test, especially for someone with lots of experience on complex aircraft.
Having about 550 hours before starting my MEP rating including about 150 hours complex time in various Arrows, I took a few minutes under 13 hours on a Seminole plus the hour long test for my initial MEP. However this was under the FAA regulations and as such I had to learn to fly it to FAA CPL/IR standards as that is what I held.
If one is going to use the Multi rating on their JAA PPL in IMC (if they have an IMC rating) then you should definately get extra training in IMC asymetric flight. Its not that difficult though but I wouldn't like to figure it out on my own if one of the donkeys quit whilst in thick IMC.
All the best with the MEP, its a lot of fun (but at the same time hard work) and you'll probably have a permenant grin upon your face whilst flying multi's.