First of all if you are getting clipping then you are overloading the preamp or you need to turn the gain down on the fast tracks input channel. If you are overloading the input it's better you are doing it to a cheap interface then your expensive Mac.
Fast Tracks don't need a driver they are class compliant the software that usually gets installed is to switch the interface between 16 and 24 bit.
At first thanks a lot for your answer and sorry for the first line of my post (buyed instead of bought)
When I say that sound is clipping it's beacause of my beat in garageband that is too strong, but with the headphone out i don't hear clips, i just see them in the track while with the fast track i hear them ...
I'm now reassured if you can tell me that the software installation in the CD doesn't touch my OSX drivers even if M-audio name this "Drivers install" on their site.
So, if i understand it's just the sys-pref button to switch 16-24 bits that is added ? nothing else.
How can i see if other drivers have been installed ?
i've uninstalled drivers and saw what wah uninstalled. Except a file named MaudioFastTrack.kext there were only software to switch 16-24 bit.
What is the .kext file ? i've rebooted , the driver is no longer installed but my sound card si always recognized et works good.
what do you think about this, do i may re-install driver or may i keep my system like this ?