THANK YOU VERY MUCH H.G.Muller, for your help and all your efforts
!!! 1) I didn't know that recent XBoard development was Linux specific.
I'm still at Debian Jessie (oldstable), and due to a known bug, Xboard can't be neither installed from repositories nor compiled from source (so wasn't informed for latest development).
Arena is an alternative solution, but personally I prefer to reboot at Windows and running Winboard.
Of course there's no reason for updates, if there's no Windows specific improvements.
2) a) For the 32-bit binary, I agree that compiling Winboard as a x64 binary won't get big performance improvements. More important is the backend chess machines (eg. StockFish) to be x64, so you'll gain the most out of your machine strength.
b) In a more theoritical approach, x32 applications can't natively run at x64 Windows, so SysWow64 comes to play.
SysWow64 being a compatibillity layer, I think it adds more complexity and performance loss.
Being invaluable for running older apps (mainly games), I think it may be avoided for running serious programs.
And as it's predecesor NTVDM, can be retired from MS at any time, as NTVDM retired without further explanations.
My personal thought is, that at future we'll need an x64 binary.
3) For the editing position problem:
a) Trying the right-click sugested methods, is what I already tried and only drived Winboard to crash here. Maybe a bug?
b) Adding at shortcut the "-pieceMenu true" argument, did the trick!!!
Please let me test it for a while and I'll be back.
THANKS AGAIN!!! EDIT:4) I tested Stockfish v.9 x64 POPCNT and seems to work perfectly.
5) The only thing that didn't work for me so far, is sounds.
The Options -> Mute all Sounds option is deselected, but the Options -> Sounds... is greyed out.