I'm sorry but I haven't really understood your reply.
The fact is I am impressed by those who say "I'm encoding "insane nmt99 tmn 450" because I've got a good hearing and I want the best".
I've decided to give braindead up.
Xtrem seems good enough to me because I didn't notice any problem on Wagner with that preset (I used my Sennheiser hd200 headphones- they cost as much as my hifi : 85 euros). On a french forum, a guy made a test-session with very very expensive hardware (about 15 000 euros). The 5 listeners didn't notice any difference between Xtrem and the original tracks (5 songs from different styles that are difficult to encode).
I think there is nothing to add ( but I would be happy to get more opinions)