You can also use a dual-controller power pack.
But what you really need to design into your plan (as I am doing now) is electrically-isolated blocks of track. If you have two loops, for example, isolate them at the crossover(s) with the little plastic track joiners. That way, you can have one controller running the inside loop and the other the outside. When crossing over, just set the controllers to the same speed. My previous layout (bought second-hand) was wired that way, and it was very simple.
There are many here who will encourage you to move to DCC, but I am in the same boat as you - I've already spent to much money on this effort, and a DCC conversion would set me back another several hundred dollars.