Key 61 Touch Strip: how to affect only audio track(s) ?

Hi all !
The MPC Key 61 has a nice touch strip which can be used to add control to the single instruments.

I wonder if it can also be used to affect audio track(s), and if it is possible, how to achieve that ?

In other terms, how should I configure the touch strip in order to alter only one or more audio tracks ?

Thanks in advance,
Sergio