Hmmmmm. Where to begin.First the difference between active pre-amp, passive preamp, buffer. Active preamps are designed PRIMARILY to be able to adjust gain via attenuation (adjust volume downwards from unity gain) as well as add gain by actually amplifying the signal. Passive Pre-amps only attenuate. Buffers do neither instead they add the sonic characteristic of the said buffer into the signal by in some cases filtering out some noise, adding a bit of it's own flavor, and IMO most important being an interface in which impedance differences might be corrected, some buffers actually add a bit of gain, the Zero supposedly does not vary from unity. For more indepth descriptions our designer/builder friends can fill you in.
I'll try to explain it in as simple a way as I can, pasensya na if my translation to lay speak is not too good. There are three places in the signal path where buffer stages can be inserted. The more common is between the source component's line level output ( CD out, Phonostage out, DVD analog out) and the linestage. The other place is between the line to the Power Amp. The third is in the tape loop or EQ loop of a receiver or a pre-amp with this utility.
PROs:
It can make mass market CDPs and DVDPs sound much better by augmenting the low spec output stages built into these units.
It may be cheaper than modifying the output stage of your existing CDP with a tube output stage.
It can give you the tube sound by adding pleasurable second order harmonic distortions to counteract the primarily 1st order distortions of budget digital devices.
In effect a more refined presentation. Will it add resolution? Ultimately no but by smoothening out some of the rough transient edges some deatails may become more noticable that were previously masked.
CONS.
One more socket.
One more pair of interconnects.
Another link to the chain to add noise. (Just hope it's the noise you like
)