Hi Laurent,
I have been through exactly what you are experiencing now - well, I believe it is the same experience I had that you are having.
When I first brought the Orchestral strings, when I was playing them, I couldn't work out why I could not get it to sound so great as they did on the demo's, with all the nice smooth sounds, and the interconnectedness, and the nice even volume control levels, and the subtle movements in sound volume that you have with strings that you hear in a live performance..
It was not until I accidentally came across a post on another forum on how one does this. When I tried it out, using the adivce, I was elated.
Basically what was happenning was this, I would load a string patch, lets say legato one, and when playing it back, I was getting louds and softs and I could not control [my keyboard is only partially weighted, not a fully weighted one], the volume as I wanted to all of the time.
Lets say I wanted to play a soft melodic line - playing carefully, and trying to control my velocity was not easy. I kept getting frustrated why I could not get it to sound as a smooth melodic line. Some of the time with very carefull control of my fingers I could get a smooth sound at one particular volume level, but now and then a note would suddenly change to a different volume level due to me having difficulties moving all of my fingers with the exact same velocity.
The solution I found was
1. simply to load the sound eg a legato patch from the SE solo strings for example as either a patch or part of a matrix
2. Click on the "perform" button on the Vienna Instrument player
3. Give a left click on the velocity x-fade to turn it on
4. On the little lever strip, give it a click with the right hand of the mouse
5. It will start flashing red meaning it's ready to hook up with whatever controller on the keyboard you choose next
6. Lets say I decided to control the velocity level with my mod wheel, I just touch it and start moving it, and you should see the lever on the velocity strip move up and down exactly in syncronisation with your movements of the modulation wheel.
Now, the great thing about this is that the volume of the instrument is not controller by your fingers, but by the mod wheel. If you want it softer or louder, you simply move the mod wheel up or down depending on what volume you want, and leave it at whatever position you want it to be - from very soft, to fully loud, or somewhere in between - and the great thing about this is it does not matter how hard, or soft you hit the key - either the fast or soft velocities of your fingers striking the keys will not make the least difference to the sound. It will all sound the same level that you have moved the mod wheel to, and I think this is what you are wanting to achieve.
I hope this solves the problem. Once you get to know how to use the mod wheel, It's just fantastic to play and control the sound with the mod wheel or whatever controller on your keyboard you choose to use.
Of course, you may not want the mod wheel on all the time, you may want to switch it off and on. and for that, if you go right to the top of the "Perform" window you have opened, and click on "Map Control" instead of the "Perform Control", you will find a list in two columns - the list on the left gives you the controller you want to choose to switch something off or on, and the right hand column gives you the list of controllers eg
Expression
Master attack
Master filter frequency
Master release
Pitch
Release Samples on or off
slot crossfader
Vel.xfade On/Off
Velocity Crossfader
Now, if you have chosen the mod wheel to control the velocity, you should see this text to the left of the Velocity Crossfader name showing as "CC 1". As you know already, that the mod wheel is always referred to as CC1 in midi language.
If you click on the word "none" to the left of the word Vel.xfade On/Off, then jump down the page directly under the lined graph symbol with the line going from the bottom to the top, and click on the word "none", a menu bar will drop down saying
and
control change
note on velocity
pitch wheel
speed
This means you can pick anyone of those controllers to turn the velocity cross fade on or off. And this is handy, as you may want to use velocity cross fade on just the sustained, or legato patches, but not for staccato, or pizz patches etc. For those you may want you use your fingers controlling the volume of the notes.
Now, just a warning here, if you have chosen mod wheel for the x-fade, lets say that you click on "control change", then what you will see is the words "11 Expression" which simply means that cc11 is controlling the x fade on and off - as well as the expression controller,- which means you need to pick a different controller than the c11 setting. This means you click on the words "11 Expression" and a drop down [or should I say"drop up"?] menu with a list of all the control numbers from 0 to 127 are there for you to select from.
Now, I am not sure how people do this thing of turning the xfade function on and off while playing with a different controller - I just do this in Cubase by adding a controller message of CC2 on the controller pane to turn it on and off as I tend mostly to start with a midi score first made in Sibelius, then add the controller detail later, but I am remembering that I think Paul Steinbauer demonstrates this in the "X-fade" video that is on this site, or, I am pretty sure the dvd's come with the installation DVD's for you Vienna Instruments.
I am sorry that I took so long to explain this, but I think it is best to explain things step by step.
I hope this may help you solve the problem!
best,
Steve[:D]