Similar channel into single channel

Although it can be done with Calculations, I prefer Apply Image as you can combine the 2 extra spot channels into one of the existing spot channels without creating new channels as Calculations does.

With spot channels, white in the channel is no ink. Black is 100% ink. I guess which mode one would use would depend on how the results should look. But I would think that for spot channels you would use either Darken or Linear Burn depending on how you want to effect the intersections.

It looks like you can get the book info from the channel's Action Descriptor.

function getSpotBookInfo(){//should return an object if the activeChannel is a spot channel. Returns nothing if not
     try{
          var ref = new ActionReference();
          ref.putEnumerated( charIDToTypeID("Chnl"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") ); 
          var desc = executeActionGet(ref).getObjectValue(stringIDToTypeID('alphaChannelOptions'));
          var colorDesc = desc.getObjectValue(stringIDToTypeID('color'));
          var book = colorDesc.getString(stringIDToTypeID('book'));
          var colorName = colorDesc.getString(stringIDToTypeID('name'));
          var obj ={};
          obj.toString = function(){ return 'ColorBookInfo'; };
          obj.colorName = colorName;
          obj.bookName = book;
          return obj;
     }catch(e){}
}