If your computer has more than one sound card, you can easily switch from one to another using the Multiple Sound Card Wizard.

My laptop, for instance, has an HDMI port that is auto-selected at boot, but I want to record on the analog card, because that's where the line jack is. So when the wizard comes up, it shows both cards, and I just click the second one. Then a mixer will pop up, and you click the box beside "Master" and turn it up. Do the same for any other sliders that you want to turn on - the front line input in this case. Close the window, and you're done.

It's the same with JACK. If you have more than one audio card, then click the dropdown arrow beside "Interfaces" in Settings. Select it, click "save", and restart. This is also where you select your external devices, like your PodXT, firewire, or usb interface.

You may have to reboot for things to take effect.

Saving at shutdown saves your settings for next time, as well as anything else you have done while using Studio 13.37, whether that be recording a song or changing the wallpaper.