Have room for 4th loop, How do I wire up my DCS System for the 4th loop??

With DCS, any PS2 or PS3 loco anywhere on the layout can be controlled independently of any other loco.  That should answer your last question.  Follow instructions in the DCS manual or in Barry's book.  Setup you describe should work fine.

LJ,

  I agree with RJR no problem all P2/P3 engines are independently controlled from the Hand Held.  You do not even need another Transformer, if you already have enough power, just run the lines to the mid and outside rail of your new loop and have fun.

PCRR/Dave

You do not want to tandem 2 KWs too one loop of track.

Take 2 loops that you want to run conventional on and connect to each z-4000 throttle. Connect the other 2 loops to the KWs one each. You can use the 20volt pin or 1 throttle.

I set all 4 channels to fixed and when i want to run conventional i vary the power to the transformer. You can run the variable channels with the handheld and use throttles to control the fixed.

All 4 loops should be isolated from each other with insulating pins or just physically separated.

I have STD gauge also and run 4 loops one on each channel of 2 Z-4000s. I like the volt amp meter when running conventional.