Wiring with Lionel Power Masters

Thanks Mark - you answered my specific question and gave me a word I should've used for clarity, "daisy-chained." 

I'll have the switches insulated from one loop at the center rail (in addition to the outer rail for the non-derailing feature) so that only one transformer (or PM in this case) and loop will control the switch between the two loops.  The second transformer picks up the engine once it hits the track. I've made this work before plenty of times with conventional. 

The PM-1 "U" posts just pass through the brick, and the non-fused PM-1 adapter cable IS the "U" connection to common("U" on a ZW, Z, KW, SW, etc.).

The fused wire goes to the output A, B, C, or D(Z, ZW, V, VW, eg.) of the transformer you are using and is regulated by the PM-1 at the "A" terminal. You leave the transformer(s) turned up to full voltage, all PM-1 "A" posts are connected to center rails. This provides the proper polarity for whistle/bell operation.

In brief, you really don't need to change your common ground scheme at all, but you do need to either power each PM-1 with the two wires of the adapter cable with the unfused wires connected to any convenient common ground location, or connect the PM-1 "U" terminals to any convenient common ground location, or both(which is usually what ends up happening - redundant - but not harmful in any way).

You really only need to connect to the "A" posts on the PM-1s to the track, as long as your adapter cables and track are all connected to common.

Thanks guys.  This will save me time and cash.  In addition to my main "table top" layout with the 3 loops reference, I built an around-the-ceiling shelf layout with two totally separated loops.  I plan to hook them mup to 2 PMs, as well.  I'm starting wiring them first and will run 3 wires instead of 4.  That'll save me about 50 feet of wire.  Thanks!