I use a Z-4000 to power my layout, on which I run mainly Legacy engines but also some MTH PS-2s. The track is powered through the MTH TIU fixed voltage channel with the Legacy base attached to the outside rail. (I do not run in conventional mode except when I have to test an engine that has problems.)
I have sometimes wondered whether this configuration causes problems with TMCC or Legacy engines; certainly I have the odd smoke output problems with them but I have never noticed a coupler failure.
I've never had a smoke output problem with an MTH engine, however. That and the fact that the difference in performance shown in Mike's video is so great makes me wonder if I am missing a trick.
Since most of my engines are Legacy, should I be switching back to a modern Lionel transformer? I ask partly because I recall an MTH technical note about sine waves and early PS1 locos, which I have copied in below because it suggests that in fact using a Z-4000 to power track through a TIU results in something other than a smooth or "pure" sine wave - more an approximation of the chopped wave Mike's video refers to. I got curious about this because he does not mention using a Z-4000 with the MTH TIU, so here's the extract, with the part about TIU output in italics.
(BTW, I freely admit that I might be misunderstanding the significance of the reference below but I thought I'd ask the more knowledgeable people on the forum. However it might explain why the Lionel CW 80 is not on MTH's compatibility list and the operating issues RickO refers to in a posting above.)
Early Proto-Sound equipped engines (PS1) built in 1995 and 1996 suffered operating anomalies when used with "shark-fin" or phase control AC Waveforms found in the AC track voltage of what were then considered modern-type transformers. Older transformers, like Lionel's ZW model or MTH's then newly released Z-4000 employed a more "pure" sine wave form of current for which the PS1 system was specifically designed.
Because these newer transformers could cause the sound system to act irregularly, MTH chose to disallow operation with any transformer type affected by the shark fin wave form rather than suffer complaints that the engine was defective.
By 1997, software designers had pinpointed the shark-fin problem and resolved it through software and hardware changes in the PS1 circuit board. Consequently 1997 and later PS1 engines do not require the shark-fin transformer rejection needed in 1995 and 1996.
Users of DCS may have experienced the shark-fin rejection when attempting to run those engines on a variable channel. This is because the DCS Track Interface Unit (or TIU) does not employ the more expensive pure sine wave form of current found in the MTH Z-4000 and instead relies on the less expensive phase control AC waveform. While the TIU waveform isn't as pronounced as that found in those early mid-1990's transformers, the PS1 software will still reject the current and not allow the locomotive to leave the RESET state.