Hello,

You can use your MS2 setup to run both layouts at the same time without anything else. Just connect the 2 rails track to the brown and red you are using to the 3 rails track.
Of course the trains in the 2 rails track must support DCC, mfx or MM.
A limitation is the maximum current your MS2/Track box setup can deliver. Probably you can run without problems 1 train in 2 rails and 1 train in 3 rails. The 3rd train will be more difficult and a 4th,
probably impossible, but it depends on the current each train will need.
I only use the MS2 to run a maximum of 2 trains or 3 if they don't have many coaches or wagons.
If you have a CS2 or 3, then it will be a different story. You can run more trains simultaneously and if you use boosters, you can run a lot of them simultaneously.

Miguel