Anyone been messing around with the dual tones much?

I'm a little confused on how to get say a 12 acoustic sound and the mag pickup sound at the same time and have them both run through different effects chains...

I understand that you choose Variax 1 and Variax 2 for the input source but how do pick both a modeled setting and a mag setting?

There's probably not a way to choose which mags it's using is there? (other than the toggle switch... but doesn't that change the modeled sound too?)