top spanish language schools in madrid?

hello,

in a couple of weeks already, i am supposed to spend two months i madrid. so now, i am looking for an intermediate-advanced level (preferably full immersion) language course. the cervantes website recommends an overwhelming number of 17 institutions. further, tandem, astex, ef and international house have been recommended to me.
however, it is proving rather difficult to assess the quality of these language schools by merely looking at their websites. i would like to assure i won't wind up in one of those school that specialize in teaching students how to "get by" in ibiza (place an order in a restaurant, communicate with the cab driver and tackle grocery shopping). i am looking for a demanding, sophisticated course with thoroughly educated spanish teachers. any suggestions?

my undying gratitude for any insight :)