Been there.

I'm also bringing up a smallish layout using the Zephyr Xtra and turnouts driven by Tortoises.  During the planning stages, I'd thought about driving the Torti with a separate DC supply and dealing with switches and LEDs when I got around to doing my control panel.

Then I got to a point where I needed working turnouts and my control panel was (and still is) not yet implemented (lack of work time on the layout), so I changed my design to use a Team Digital SRC-16 decoder (which can drive up to eight turnouts and does cool stuff like automatic turnout alignment etc.), so the decoder drives the Torti and also has enough outputs (in addition to using the SPDT switches on the Torti) to handle any signaling I might want to add in the future, and can handle switch inputs from my eventual control panel to command the Torti.

The SRC-16 can run off track power or it can run off a separate DC supply and get commands via LocoNet -- right now mine is on track power but eventually it'll sit on the Zephyr's LocoNet.

If you want to stick with the Digitrax decoders, that'll still let you control the Torti, but you may have to run your signaling through the SPDT switches.

The DCC route is sort of the lazy man's approach, but it did let me get stuff working quickly (and gives me more things to play with later on . 

Excellent treatise, Don!