Hi Vadim,
sorry, I was almost missing to answer you...
Search by multiple tags... good question!
First of all, take into account that we are developing a brand new api, and one of the big enhancements is exactly on the search by tags: there will be full support for multiple tags boolean and fuzzy search, some synonymity and hierarchy, nested tags entity, highlighting, etc... If you can wait few months you'll get all of this!
However, search by multiple tags is somehow supported also by the old get2 api. You just missed the "tagmatchingweight_desc" order value in your query. Look to this one, it should be what you need.
http://api.jamendo.com/get2/artist_genre+album_genre+id+name+stream+artist_id+artist_name+tag_idstr+stats/track/jsonpretty/track_album+album_artist?n=50&order=tagmatchingweight_desc+listened_desc&tag_idstr=ebm+darkwave
As you can see there's also the "stats" select part to give you back the listens and downloads count.
Note that even if possible to put "tag_isdtr" in the select part of the query, it will return just one tag. That's a limitation due to the underneath implementation (nb, it won't be like that in new api), but as you can see, the (at the moment) first returned track has actually the 2 tags you were querying for:
http://api.jamendo.com/get2/track_name+track_id+tag_idstr/track/jsonpretty/track_tag+track_album+album_artist?id=248928
Have a good programming!
Claudio