… Is there another way to make my Bass parts always sound an octave lower than written, other the the Expression Tool > Technique > 8vb? …

Indeed there is.

There are at least two ways:

1) Change the clef to the {Bass Clef character with an 8 below it}.

If you do not need to display the ‘8’ below the Bass Clef, then use the Clef Designer to edit the clef, and replace the clef’s character with the ordinary Bass Clef character (without the ‘8’).

2) You can use the Staff Tool to add an octave transposition to the Bass staff (do you need instructions for this?).

In the Document menu you can select the options

Display in Concert Pitch

and

Keep Octave Transposition in Concert Pitch

Or choose a sound file in which the bass always sounds an octave lower than written.

If you define the bass in the Scoremanager, the audio will be transposed an octave down compared to what is written.

You don't mention your version of Finale, but in recent versions, you can even display that transposition in the concert score (Document -> Keep the Octave Transposition in Concert Pitch).

Longtime Finale users know that it took many years for Coda Music to get this right — and they did. As you see, there are a few ways to skin this cat.