Try using the implode music function from the utilities menu. Highlight the Sop & alto, run implode music. Then do the same thing with the tenor & bass.

The other option is to copy each staff in a separate layer to the destination staff, then run the merge layers plugin.

Implode works but it took some extra effort because I am working with two scores.  The original SATB should not be modified so I need to copy the parts to the piano score.  First I implode so that soprano and alto are combined in the soprano staff of the original score, then I copy to the treble clef directly to the piano score, then undo the implode in the SATB score.

Regarding the merge layers comment: That is what I was trying to do but with no success.  I copy the soprano part to layer 1 in the second score, but when I try to copy the alto part to layer 2 it simply overwrites the soprano.  The same thing happens when I am working in only one score.

Maybe I am missing something, but isn't there an quick and efficient way of copying two independent melodies to different layers in a single staff?

I have no trouble doing this with JW Staff Polyphony. But you can try the "long" method:

Soprano in staff one, layer one. Alto in staff 2, layer one.

Move alto to layer two.

While in layer two, Document menu > Show Active Layer Only (your soprano notes will vanish!)

Select the alto staff, and drag it into staff one.

Document menu > DESELECT Show Active Layer Only

Delete the original alto staff

Thanks, that's another solution that works. 

Why can't we just choose SA & TB arrangement? That's the way most choral music is sold. S + A in the treble clef and T + B in the bass clef. Why have to jump through all the hoops to do what most printed music is sold as?

Jon Covey,

Did you try the plug-in JW Staff Polyphony?

I haven't tried it yet. After reviewing previous comments, it looks easy to do. This is a big help.

I've been using Finale for practicing the tenor part for the choir. As a baritone, I can choose either tenor or bass. Of course, I can't do basso profundo, but most choral music doesn't often go much below E2. Choir directors prefer for me to sing tenor.

Lately, I've learned Finale can do much more. especially with a DAW and EastWest Hollywood Choirs. This is lots of fun. I'm still working on Handel's Messiah Chorus, but WOW.

I don’t understand what you mean by

“Why can't we just choose SA & TB arrangement? That's the way most choral music is sold. S + A in the treble clef and T + B in the bass clef. Why have to jump through all the hoops to do what most printed music is sold as?”

I think there is already a template for SATB (on two staves) with Piano. Is it the note entry that’s giving you the problem?