Squirrely problems require climbing all over the thing and trying things that make no sense to lesser mortals.

I assume, but you don't state, that in all cases you are running the source through the Zektor piece.

What model Zektor piece is that, exactly?

Is its firmware up to date? The firmware of the TV? Of the BD Player?

What audio adjustments does the Zektor piece have?

What sources do you have other than the two BD Players? Do they work correctly?

After your hoped-for victory with the frist disc, did you switch the discs from player to player to verify that the discs and the players always work the same? (Two is not "always" but it's more informative than one.)

There's no setting on a disc where the sound would play correctly with someone with just a TV. But did you actually connect one of the BDs to a TV with only an HDMI cable? And then you tried the other one?

Maybe someone from Zektor can jump in here and make some suggestions.