In the FireWire audio standard, there can only be one "master" controlling a specific audio interface at any given time, either the host computer or the Paca(rana).
Some audio interfaces (notably the MOTU and Apogee FireWire-based interfaces) let you switch "masters" relatively easily, using Audio MIDI Setup on the Mac, or the Device Manager on Windows, so you can be using the audio interface either with Kyma or the host computer audio software (but not both simultaneously).
However, the drivers for most manufacturers' audio interfaces require installing or removing the driver and restarting the computer in order to make this switch. Because of this, most people end up dedicating one interface to the Paca(rana) and one to the host computer, connecting the two interfaces via a digital connection, like ADAT.