AFAIK Finale does not proved a col' 8ve feature. One can certainly create the notation but would have to use a work-around to realize the audio for it.

That's what I wound up doing. I created a 2nd piano part for the octave doubling. It would be nice if Finale could do that simple notation and playback...and handled different dynamics for treble and bass clefs in the piano.

If one sends the various voices in the left and right hands to separate VST instances in the Score Manager and Devices list, one can have different dynamics in the various voices/staves of a piano composition. Just because the piano initially defaults to a single MIDI channel does not mean one has to leave it that way.

One might in that case, however, need to use separate, hidden dynamics when one wanted both staves to act together.

This is what I do now, after realising that Finale didn't give me different dynamics for piano.