Good comments above lots of detail.
You might be interested in what MTH had to say when they first released the Proto 3 system for us on 2 rail engines;
from the MTH website;
Since Proto-Sound 2.0's introduction in the Spring of 2000, a few subtle changes have been incorporated into the basic board design including; a different power supply, the ability to operate on AC or DC power, the inclusion of wireless tethers, flash onboard memory, improved microprocessors and improved sound amplifiers.
Regardless of these changes, a year 2000 Proto-Sound 2.0 equipped locomotive runs exactly the same way under the DCS Digital Command Control system as a Proto-Sound 2.0 board built in 2010. You simply put 'em on the track and run 'em.
And so it is with Proto-Sound 3.0. Like the different iterations of the Proto-Sound 2.0 boards built over the past decade, new O Gauge Proto-Sound 3.0 equipped locomotives operate exactly the same way as their 2.0 counterparts. This means they will operate together with 2.0 engines on the same track at the same time when controlled by DCS.
They will operate the same with any compatible conventional AC transformer as 2.0 engines.
They can operate on AC or DC power.
They feature the same conventional control features and include the same command control features.
Most importantly, no new equipment is required to enjoy any feature found inside a Proto-Sound 3.0 equipped locomotive.
Like all evolving technological products, there are a number of new features found inside each Proto-Sound 3.0 equipped locomotive that we believe will continue to ensure that M.T.H. locomotives are the most advanced, most universally compatible and most exciting to operate in all of model railroading.
Chief among these new features is the inclusion of a NMRA Digital Command Control (DCC) receiver. While not a popular command control choice of O Gauge model railroaders, DCC is the dominant command control protocol in other scales, including HO, N, G and 2-Rail O Scale.
By incorporating a DCC receiver into our products, your new Proto-Sound 3.0 equipped locomotive can be operated in command control mode using any DCC controller available today. There are dozens of DCC controllers available from a large number of DCC controller manufacturers. Many of these devices can control all 28 different DCC functions found in every M.T.H. Proto-Sound 3.0 equipped locomotive.