If you want to run two trains, do you need to have to IR controllers? Or can you just set different channels for the different trains and run them all with one?

Steve

You can run 2 trains per channel, red and blue so in theory with out mods you can have 8 going at once all off one control

Note also that you can change which of the four channels the remote is on at any time without interfering with any of the running trains. So you can (with a little effort) actually control all 8 possible trains from a single remote if you want. Does get a little more tricky to quickly stop one if that's important though (although not necessarily more so than swapping which remote you're holding I guess!)

I run four trains on two controllers, and stick them together using technic pins. I use 1x2 plates on the controllers in the color of the train to make it easy to distinguish which knob to turn.