I do not think you want to change "banks." Unless you intend a separate instance of Aria for each sound create (very inefficient in most cases) you want a single bank within which you use different MIDI channels to access the various slots within the Aria Player.

So if I load all the grouped sounds such as Hauwptverk two times in the bank then change the volume to two positions and the same thing with the Brestwerk two times and volumes, this will get me my melody swapping between the two keyboards for the mp/mf two episode needs.  I got that!  So, how do I apply the 32' Pousanne or Faggato to the mix for the pedal at the end?  At first this seems a Bank issue but it appears a Bank cannot be applied without including a channel and I need multiple channels. 

..and how do I get the software to change banks/channels during the course of playing the composition?

Load any "extra" sounds you need in unused midi channels in the Aria player.

To get Finale to change midi channels, you need to create a text expression to do that. This text expression can have any name, such as "switch to channel 9". You can make this expression hidden in your score if you don't want that to print. In that text expression, you need to define the playback action as a midi channel change. Go to the playback tab, choose "channel" from the pulldown menu, enter the midi channel number. Assign this expression to the correct spot in you score and Finale will change the playback sound.

Terry,

It is important for us to know whether you are trying to get Finale to play via Garritan sounds or through your church organ. To do the latter may well be possible (there are some youTube videos of people using MIDI to drive a MIDI-equipped church organ), but to do that, you will need someone in your area more familiar with your organ's MIDI setup than anyone here is likely to be (or to work on for free).

As Jeffrey has said, you can use text expressions to change an instrument (manual) mid-composition. I would add that you can change to a channel that drives multiple slot of the Aria Player to layer organ stops by using the pull-down menus I indicated above to set several slots to the same MIDI input channel.

You guys are awesome!  I thought the bank numbers were computer set so didn't think about the potential to change them.  I have accomplished three settings on three keyboards, too.  Now I'm off to establish all the pistons I need then pursue the changing channels mid-composition.  Ever grateful.