Buffer pre or active pre...

What is the trade off between two?.

How about the details, layering..etc?
When you say buffer pre, you are talking about an active preamp, the buffer being an active component. Do you mean a unity gain (no gain) buffer preamp vs. one with gain? Or, are you confusing active vs. passive (no amplification stage or buffer stage, just switching and attenuation).

Most source components, other than phono gear, have enough gain so that only attenuation to control volume is really needed. The buffer takes away some of the concerns over proper impedance matching of source components and compatibility with the downstream amplifier. If you don't really need more gain, a buffer stage is simpler, cheaper and should provide the flexibility/component compatibility that you need. Either active buffer or a preamp with gain will be less prone to suffer from compatibility issues or from a loss of "life" (dynamics) than passives.

My only unity gain linestage was the Placette active that I owned. One certainly cannot say that it suffered from any loss of dynamics. My current linestage is a tube linestage with 13 db of gain. I actually need the gain with my current phono setup.
No, it's not about passive pre.

it's about the same amplifier design which has 4 6922 (active) and another one with 2 6922 (buffer).

I don't know how to call this buffer or buffer with gain but certainly the 2 tubes need a little more crank of volume to sounds like 4 tubes.
Regardless of the terminology the manufacturer's literature may use, both amplifiers are active. An active device in the context of amplifiers is a tube or transistor. It is the opposite of a passive device, which can refer to a resistor, capacitor, inductor, transformer, switch, etc.

The buffer amplifier has, presumeably, a gain of one, or very close to it. The amplifier with four 6922's presumably has a gain considerably greater than one.

The two-tube amplifier "needs a little more crank of volume" than the four-tube amplifier simply because it has less gain. It's hard to generalize beyond that.

-- Al

It appears that you are talking about an active buffer linestage with unity or close to unity gain vs. an active linestage with some gain. If you don't need the gain, the simpler circuit should sound better. The buffer linestagestage, if well designed, would not be distorting at or near full output.

Because this is a tube unit, I would guess that the circuit is a cathode follower (to keep output impedance reasonably low). I have no personal bias myself, but, some people don't like that kind of circuit, so, the issue of whether a passive would be more desirable becomes more of an issue (assuming, again, that gain is not needed). Passives have their own issues, so, the choice becomes an issue of system compatibility and tradeoffs.
Thanks all..

These two pre are based on MFA ref MC one. My friend made this with high quality printed circuit board (great skills he got).

OK, about the gain I think I don't have any issue. I'm using VTL MB250 signature (250wpc) with Naim CD5/Fcap2. After extensive listening I still can't make up my mind on which to go.