If you're on Mac you can create an aggregate device using the "Audio Midi Setup" application. For example, you can connect a Toneport, a US-122, and a Firepod to get 4+2+10 inputs, here's how it's done:
http://www.apple.com/pro/techniques/aggregateaudio/
(@Windows users: Is there really still no way to do this in Windows with ASIO drivers??)
To run the Gearbox plugin you just have to connect a Line6 device (e.g. PODxt or Toneport) to your computer. It just works as a dongle, you don't have to record or playback through it.