I noticed the same thing when I was mucking about with the Soviet Waterway mod a few years back.
IIRC, the various Schuka's (plus the S class!) and anything that shares the same interior model all have the double voice problem.
What I discovered to be the cause is the figure repeating the helm orders not only appears in the Control Room, but he's
physically duplicated in the Engine Room, as far as I can remember. I only discovered that by using the free cam to have a roam about the interior.
So it's the same model, using the same animations, literally being in two places at the same time.
I can't remember exactly what I did to try and fix it, but I
think I opened up the interior model in S3D Editor and deleted the model placement node in the engine room in order to physically remove the duplicated figure.
It has been a few years however, so caveat emptor!
Mike.
Big Fat EDIT: Luckily I still have the various files stashed on my PC, so I've been able to see and remind myself of what I did.
I
didn't delete the character node, I went into it's sub node calling up the animation file the figure uses and changed
that. So the figure in the engine room is still there, but he now uses a
different animation from his compatriot in the Control Room. By the looks of it, I borrowed the expanded GE Anim files that Ducimus created for his Nine Delta Two Mod.
This was way back in 2016 judging from the file dates, however I can't remember the exact details.
I hope that's of some help!
Mike. (again!)