The A5 has input and output volume controls, but the impedance level has to do with the electrical properties of the signal, not the volume.
I know that you can line out from a pre-amp to a recording line in, but I don't know if the A4 (bass) or A5 (guitar) pedals knock down the impedance, or if it carries the same properties all the way to the amp.
On that note, does anyone have any idea how to contact Korg tech support? This seems like the kind of question that could be answered in 5 minutes by someone at the company itself.