Never, ever believe that your ears are not enough... They are definitely, more than enough. Sorry, forgive me for waxing back to the days when I was a recording engineer, but...

A meter is really only a convenience, it only verifies what your ears can and will tell you. Imagine the very first meter, (I wasn't there) but we can imagine increasing the gain until the signal distorted... Then drawing a line at that point saying "this is where things go bad". Now allowing for percussive attacks and allowing some space for those spikey attack transients... You have a metering system. Based on when the Ear says "obviously, that's too much".

A compressor is an amplifier that the more signal you put in the less you get out, once you exceed the point called the threshold. It reduces (Gain Reduction) those spikey transient peaks. The result is, because these peaks are reduced your signal will not reach the point of distortion. This brings the highest peaks down closer to the average level. So you can now raise the overall level without worrying about that distortion. This can give the signal more "presence".

Properly used you want to simply slightly reduce the loudest peaks (particularly on a percussion instrument like piano) just enough to give a full rich sound on the piano. An over-compressed signal sounds wrong, wrong in that it is unnatural. It begins to sound "squashed" almost inside out... Here's what I mean:

On a vocal, compressors are used to reduce the loudest peaks so that they are closer to the softest words. It compresses the dynamic range... So the "shout" is not so very far away from the "whisper". But when they are too close together, it sounds out of balance. The softest words (whispers) go by uncompressed, while the shouts get gain reduced. When you overcompress a vocal things like breath intake and lip smacks sound HUGE and the big notes sound small. It's not that they are softer than the breathing sound or lip smacks, it is just so obviously out of balance from what you'd expect, naturally.

You know you have too much compression when you can hear it! The singer will sound like they have emphysema simply because the normally soft intake of air is not so distant in volume from the full on note.

Now, a multi-band compressor allows you to treat the different frequency bands separately... It not only senses the incoming signal but is sensitive to the frequency range. On a piano the "whisper" and the "shout" are concepts that you must translate on your own based on the piece of music. Is it one that has this wide dynamic range? Are certain passages not "present" enough in the mix? In fact, is the multi-band compressor even necessary to accomplish what you need?

These are the questions you must ask yourself... Perhaps just a well setup EQ is all you need.
There are no settings anyone can really give you, because the settings (for EQ and/or compressors) are so very dependent on the player, the music and the instruments in the ensemble. But always, whatever you decide, it is your ears that must be the final judge.

If the meter says you're Right... But your ears tells you it's Wrong ... Who you gonna believe?

Hope that helps.

Ok,got that ;))
İt would be nice though to have some presets ,that u can use as a starting point ....especially for something as complex as a muliband comp !!!
Thanks again for your time and expertise.