5/4 Update (Hey, Star Wars day, eh?):
I'm finally removing the outdated RailSounds 1.0 from my 18005 Hudson from 1990 and upgrading it to a can motor via Frank Timko. It will get things like fan smoke, Super Chuffer, etc. as well, but the HARDEST part is finding a suitable RailSounds card for it to do it full justice. ERR doesn't offer steam sounds that sound like a New York Central Hudson, and all of Lionel's old Hudson RS4.0 sound boards are impossible to find.
What I DID find is Lionel is now offering their modular Legacy sound boards (non-Lite boards I mean, which are essentially the same as the ERR sound boards), RailSounds 6.0 as they call it, for sale as parts. This includes both the Vision 700E and the 4-4-2 Atlantic boards. The latter would suit this engine excellently, and I will be purchasing the 5344 board for my 18056 Hudson (which is numbered 5344).
But before I seal the deal on these boards, I want to know if they're as compatible with the 691PMB2A02 RailSounds powered motherboard as the earlier 4.0 and 5.0 boards were?
And if I was to put a 6.0 board in a 5.0 RS modular system, would that be an issue? - By that I mean placing the 6.0 board in the 38097 PT tender Lionel offered for Century Club 2, which had RS 5.0.
The 6.0 boards look similar, but not quite the same as those older boards. These boards are far from cheap, but I want to do my favorite railroad and favorite locomotives as much justice as I can.