I have only used Reason and Live in one-track-at-a-time tracking situation... can you advise on how I could control them both simultaneously in a live situation, using an EMU XBoard keyboard and a Korg PadKontrol or similar?

What I'm confused about is how I tell Reason's instruments which controller they should respond to, any on which MIDI channel.

For example, say I want to use the Xboard to control each of several synths in Reason, can I switch the instrument I am playing by changing the MIDI channel? I cannot see how I can specify which MIDI input channel gets routed to which instrument...