Finally got a chance to check out a SPROG unit at a local train store with an assist of my friend Jerry C. Here is a summary of what I learned today along with some thoughts about a potential solution for my module layout.
Simply put, beyond getting the Windows 8.1 driver loaded for the SPROG-IIv3 unit that we used, everything simply worked as we would expect. The set up wasn't special, just a long (by Z-standards :0) straight test track with the SPROG running off a 12 volt, 1.25 amp power supply feeding one end of the track. I used a small Acer 2-in-1 tablet PC running JMRI with the SPROG's control port connected to the PC's single USB 2.0 port.
Switching between normal operation and programming was accomplished solely within the JMRI software. This was fine for our test setup as long as we took care not to have more than one loco on the track during programming. I didn't have WiFi available so I couldn't check it out with WiThrottle but I wouldn't expect anything different in operation from when I used that with the NCE system tested earlier.
So, given that I did go with the SPROG system, here is a potential plan for the configuration that could power and control the inside mainline and the freight yard district. The outside mainline for now would remain a DC-based mainline.
Below is a diagram of a proposed configuration. The primary DCC controller is shown to the lower left ... while the unit shown is a 3 amp SPROG 3, a lower-rated 1.25 amp SPROG-IIv3 unit is all that is needed just to run the programming track and as the control feed to the two boosters shown on the right. The boosters would have a capacity of 3 amps each and as shown, the SPROG-IIv3 is powered by a pass-through from one of the boosters.
The programming track can only be used offline, i.e., the mainline would not be controlled while the DPDT switch routes the output of the SPROG-IIv3 to the programming track. This doesn't mean that trains can't be running on the mainline while the programming track is in use but if that is done, you do run the risk of a mishap on the mainline as control access to the engines is lost while the switch is in the programming track position. At this point, I would be willing to live with this limitation in order to not have a separate programming unit.
The SPROG-IIv3 would be connected to the tablet PC mentioned earlier running JMRI and wireless control would be supported with WiThrottle and cell phones running compatible throttle apps (e.g., Engine Driver).
Independent of which DCC system I go with, I'm contemplating having the programming track actually being part of the service yard on the Central End. If I do this, I'll include the appropriate isolation track arrangement to assure no electrical mishaps occur when set in the programming state. More on this later if I don't change my mind and go with an off-layout programming track.