I recently sucessfully flushed out my clogged matrix on my 190e 2.6 using a citric acid solution. Here, where I live in France, I bought some Adritt descaler tablets from a supermarket called Lidl. I used two tablets (the size of small dishwasher tablets) in a pint of boiling water and left the solution in the matrix for an hour before flushing out with a hose and air. The result, a heater that burns! I'm sure that any descaler products that are made for coffee machines, kettles and the like and contain citric acid will work. Gaggia make a good one.
Good luck
Chris