Hope you've solved your issue by now, but if not, here's a few answers on your points.
* Is the Wwise Unity Sample downloaded (PC) version editable?
Yes, definitely. You are getting the actual source project, so you can add whatever you'd like or remove anything you'd like.
* If I attempt to make a volume change in a region It does not change the volume of the music in Unity. It seems to me as if the NEW REGION music is not being received in UNITY.
Take a look at your new music's Output bus and see if it's routed to the Music Audio Bus. The volume slider in the WAG menu will be referenced using an RTPC to specifically that Audio Bus.
* are there additions that need to be made to the SoundBanks to allow the Unity game to play the NEW music.
No, not really. You can import any music track, either to an already existing music segment or create a new one and add it to the Music_Region Event, and then after generating SoundBanks, it should be able to play it in Unity.
* Where should the SoundBanks be attached in unity (akBank).
Right now, the soundbanks are loaded from the game objects within the Wwise game object, but you can easily add an AkBank component to any other game object and load it from there. Just create a new empty game object, add an AkBank, set it to Awake, and then select your new soundbank. This is probably set up correctly, since it works on your mac.
* Are there akEvents that need to be added to objects in the unIty game?
Right now, the music is posted from a Wwise-Type and not an AkEvent. Check out the Manager game object > GameManager script > Music Start_Region Wwise-Type property and see if anything is selected in it. If not, then reselect the Music_Region Event and it will be posted when the game starts. But then again, if it works on mac this shouldn't be a problem.
Shouldn't this work as expected on BOTH platforms?
Yes, definitely. It does sound strange... I would probably start by deleting the SoundBanks (including the wwiseIDs) then generate again. If that doesn't fix it, I would check any kind of source control for whether some DLL's that haven't been transferred properly (unless you are using an external harddrive). Maybe try to check your different platform settings like conversion settings, platform voice limits, and any properties that have been included/excluded on the windows platform.
Hope this helps or you've solved it by now, else, let us know :)