Hi bja
One of the reasons your head spins is that we all do it slightly differently and a lot has to do with the size/complexity of our the layout.
Jim in the post above, gave you sound info. There is a lot of latitude to do what you want to do. It is actually simple.
First. Legacy is more sophisticated for form of TMCC. The cab2 works with Legacy. The cab1 primarily a TMCC tool works with Legacy as well, to a limited degree. Track Power controllers [tpc] are a more sophisticated form of Powmaster. Legacy and TMCC allow you to connect to them each with an increasing level of difficulty.
THIS IS MY OPINION.
What you want will cost $$$. You have the transformers. The size of your layout would be the next question. You probably only need TMCC. A cab1/command base set offered occasionally on the buy/sell forum but certainly on ebay would do the trick. A TPC would be next. They come in two sizes, 300 watts and 400 watts. The 400 watt version tends to be more available. Three loops, three TPCs set to Conventional running. The wiring is straightforward, though there will be questions, of course. Transformer thru to the TPC thru to the Track connections -- power and common. The command base connects to the TPC and has its own power source, a wall wart --and data commands from the base to the tpc unit.
The PW ZW is either a 250 or 275 watt unit. It may be enough to power your layout again depending on size. Stay with it for starters. The ZW is wired to the TPCs. Each tpc has a code you set up. Tr1, Tr2, Tr3. If the ZW doesn't have enough power for running, then add one of the other transformers to the mix or all three. These are older models and have some unique wiring that you must be aware of since you own them.
Power up the ZW. With the hand held, you select Tr1, power goes to that oval. Run your train. Some additional commands -- YOU WILL ACTUALLY HAVE TO READ THE MANUAL FOR THE COMMANDS -- to send commands that alert the second TPC to wake-up, Tr 2 and off to the races on the second oval. You must read and understand how to manage the speed of oval one while you are working on oval two or you could have a train go off the track.
Get the TMCC unit - Command base and Cab1. Get TPCs not Powmasters. Limit the number of the transformers you use. Some of the older ones, TW and 1033 might serve you better for accessory power.
Hope this helps.
Ralph