Opportunity to buy the best Preamp... but which?

I think the guy's asking about "the best preamp" rather than "my preamp":)

In this light, I suggest you consider: for tubes the Art (which you referenced), the big Aesthetics, and perhaps a CAT.

In SS, the FM acoustics. Maybe the MBL or the Burmester...

Mikelavigne makes a point about the Dartzeel pre linked via bnc to their amp.
I had a unscientific experience listening to orchestral music, with that pre:

The Dartzeel 18 vs the FM acoustics 255: the 255 was better driving a Dart amp (more sense of immediacy and urgency in the music). BUT the Dart connected via bnc to the Dart amp was as satisfying as the FM-A

Mike --
the Dart was similar to the FM in the mid to upper mid range. In the high frequencies, the FM showed more energy. Note that where details of the music were concerned, the Dart did not require you to "strain your ears" i.e. the Dart+Dart was not musically lossy or lacked homogeneity. Cymbals for example had more energy and slower decay (i.e. they were perceptibly present longer) with FM.

Also please note that the speakers were adequately set-up and the amplfication homogenious enough in both cases so there where no aberrations such as, the percussion being in front of the violins in an orchestra, for example...

Riaa: haven't made the comparison, unfortunately. The FM (122 in this case) has 2 user user-controlled de-emphasis pots in front which allow versatility -- but would probably complicate comparisons (unless maybe if set flat on the FM?)!
Cheers

I recall FM Acoustics now...it's a swiss boutique manufacturer catering to the exclusive "money is no object/sound is second" club.

Hardly. It's a pro equip manufacturer, it's not priced over all others, and the sound quality is superb. Nice quote however.
Likewise, atma's pre is also superb sounding, and the latest CAT is also nice.
Many nice products out there -- to little money.

But now there is a MBL dealer in my country , what about the MBL preamplifiers 6011D or 5011

In absolute terms, the 6011 then the 5011.

But, I really can't tell what you need: i.e. both are very versatile and practical with lots of functionalities and... good. So, you may not need a 6011.
Both are exquisitely engineered by the way.
I would also *assume* both are better than the Capitole's embedded pre... but don't know. Really, you must try them.